Search

This study examines perceived family communication culture, social identity, development of communicative self-efficacy, and reported risk behaviors for adolescent girls. Twenty-five women between the ages of 18 and 20 were interviewed and transcripts were analyzed using grounded theory (Strauss & Corbin, 1990). The results suggest that there are indeed links between family communication culture, social identity, communicative self-efficacy, and risk behavior. Implications for future research and practice are discussed. [ABSTRACT FROM AUTHOR]

Abstract Background Immune thrombocytopenic purpura (ITP), a condition characterized by autoimmune-mediated platelet destruction and suboptimal platelet production, is associated with symptoms such as bruising, epistaxis, menorrhagia, mucosal bleeding from the gastrointestinal and urinary tracts and, rarely central nervous system bleeding. The aim of this research is to develop a conceptual model to describe the impact of ITP and its treatment on patients' health-related quality of life (HRQoL). Methods A literature search and focus groups with adult ITP patients were conducted to identify areas of HRQoL affected by ITP. Published literature was reviewed to identify key HRQoL issues and existing questionnaires used to assess HRQoL. Focus group transcripts were reviewed, and common themes were extracted by grouping conceptual categories that described the impact on HRQoL. Results The literature synthesis and themes from the focus group data suggest that decreased platelet counts, disease symptoms, and treatment side effects influence multiple domains of HRQoL for ITP patients. Key areas affected by ITP and its treatments include emotional and functional health, work life, social and leisure activities, and reproductive health. Conclusion ITP affects various areas of HRQoL. This conceptual model will help inform the evaluation of therapeutic strategies for ITP.

Kelp forests and urchin barrens are two stable states in rocky reef ecosystems, each providing unique ecosystem functions like habitat for marine species and primary production. While studies frequently show that kelp forests support higher levels of some ecosystem functions than urchin barren habitats, no research has yet compared average differences. To address this gap, we first conducted a meta-analysis of studies that directly compared the ecosystem functions, services and general attributes provided by each habitat. We also compiled individual studies on ecosystem properties from both habitats and qualitatively assessed the benefits provided. The meta-analysis included 388 observations from 55 studies across 14 countries. We found that kelp forests consistently delivered higher levels of ecosystem properties such as biodiversity, species richness, abalone abundance and sea urchin roe quality. Urchin barrens supported higher urchin density and crustose coralline algae cover. The qualitative review further supported these findings, showing that kelp forests ranked higher in 11 out of 15 ecosystem properties. These findings can help guide decisions on managing rocky reef habitats and demonstrate the benefits of preserving or expanding kelp forests.

Marine heat waves (MHWs) are extended periods of excessively warm water 1 that are increasing in frequency, duration, intensity, and impact, and they likely represent a greater threat to marine ecosystems than the more gradual increases in sea surface temperature. 2 , 3 , 4 Sponges are major and important components of global benthic marine communities, 5 , 6 , 7 with earlier studies identifying tropical sponges as potential climate change "winners." 8 , 9 , 10 , 11 In contrast, cold-water sponges may be less tolerant to predicted ocean warming and concurrent MHWs. Here, we report how a series of unprecedented MHWs in New Zealand have impacted millions of sponges at a spatial scale far greater than previously reported anywhere in the world. We reported sponge tissue necrosis 12 and bleaching (symbiont loss/dysfunction), 13 which have been previously associated with temperature stress, 6 , 12 , 14 for three common sponge species across multiple biogeographical regions, with the severity of impact being correlated with MHW intensity. Given the ecological importance of sponges, 15 their loss from these rocky temperate reefs will likely have important ecosystem-level consequences., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Genome mining of Ascomycete sp. F53 (F53), a fungal endophyte of the traditional Chinese medicinal plant Taxus yunnanensis (Chinese yew), revealed 35 putative specialized metabolite biosynthesis gene clusters, one of which encodes a rarely seen tandem polyketide synthase pathway with close homology to azaphilone biosynthesis pathways. A novel compound, lijiquinone 1, was subsequently isolated from F53 and structurally and functionally characterized. The m/z 385 [M + H + ] + compound, comprised of a cyclohexenone side group attached to a core bicyclic ring, displayed cytotoxicity against human myeloma cells (IC 50  = 129 μM), as well as antifungal activity against Candida albicans (IC 50  = 79 μM) and Cryptococcus albidus (IC 50  = 141 μM). Our results suggest that enzymes encoded on the lij gene cluster are responsible for the synthesis of 1 and that the medicinal properties of T. yunnanensis could be partially mediated by this novel azaphilone. This study highlights the utility of combining traditional knowledge with contemporary genomic approaches for the discovery of new bioactive compounds., (© 2020 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.)

The honey bee worker gut hosts a community of bacteria that comprises 8-10 core bacterial species, along with a set of more transient environmental microbes. Collectively, these microbes break down and ferment saccharides present in the host's diet, based on analyses of metagenomes, and metatranscriptomes from this environment. As part of this metabolism, the bacteria produce short-chain fatty acids that may serve as a food source for the host bee, stimulating biological processes that may contribute to host weight gain. To identify metabolic contributions of symbionts within the honey bee gut, we utilized a combination of molecular and biochemical approaches. We show significant variation in the metabolic capabilities of honey bee-associated taxa, highlighting the fact that honey bee gut microbiota members of the same clade are highly variable in their ability to use specific carbohydrates and produce organic acids. Finally, we confirm that the honey bee core microbes are active in vivo, expressing key enzymatic genes critical for utilizing plant-derived molecules and producing organic acids (i.e. acetate and lactate). These results suggest that core taxa may contribute significantly to weight gain in the honey bee, specifically through the production of organic acids.

Tropical tuna fisheries are among the largest worldwide, with some having significant bycatch issues. However, pole-and-line tuna fisheries are widely believed to have low bycatch rates, although these have rarely been quantified. The Maldives has an important pole-and-line fishery, targeting skipjack tuna (Katsuwonus pelamis). In the Maldives, 106 pole-and-line tuna fishing days were observed between August 2014 and November 2015. During 161 fishing events, tuna catches amounted to 147 t: 72% by weight was skipjack, 25% yellowfin tuna (Thunnus albacares) and 3% other tunas. Bycatch (all non-tuna species caught plus all tuna discards) amounted to 951 kg (0.65% of total tuna catch). Most of the bycatch (95%) was utilized, and some bycatch was released alive, so dead discards were particularly low (0.02% of total tuna catch, or 22 kg per 100 t). Rainbow runner (Elagatis bipinnulata) and dolphinfish (Coryphaena hippurus) together constituted 93% of the bycatch. Live releases included small numbers of silky sharks (Carcharhinus falciformis) and seabirds (noddies, Anous tenuirostris and A. stolidus). Pole-and-line tuna fishing was conducted on free schools and schools associated with various objects (Maldivian anchored fish aggregating devices [aFADs], drifting FADs from western Indian Ocean purse seine fisheries, other drifting objects and seamounts). Free school catches typically included a high proportion of large skipjack and significantly less bycatch. Associated schools produced more variable tuna catches and higher bycatch rates. Fishing trips in the south had significantly lower bycatch rates than those in the north. This study is the first to quantify bycatch rates in the Maldives pole-and-line tuna fishery and the influence of school association on catch composition. Ratio estimator methods suggest roughly 552.6 t of bycatch and 27.9 t of discards are caught annually in the fishery (based on 2015 national catch), much less than other Indian Ocean tuna fisheries, e.g. gillnet, purse-seine, and longline.

Natural product drug discovery has regained interest due to low production costs, structural diversity, and multiple uses of active compounds to treat various diseases. Attention has been directed towards medicinal plants as these plants have been traditionally used for generations to treat symptoms of numerous diseases. It is established that plants harbour microorganisms, collectively known as endophytes. Exploring the as-yet untapped natural products from the endophytes increases the chances of finding novel compounds. The concept of natural products targeting microbial pathogens has been applied to isolate novel antimycobacterial compounds, and the rapid development of drug-resistant Mycobacterium tuberculosis has significantly increased the need for new treatments against this pathogen. It remains important to continuously screen for novel compounds from natural sources, particularly from rarely encountered microorganisms, such as the endophytes. This review focuses on bioprospecting for polyketides and small peptides exhibiting antituberculosis activity, although current treatments against tuberculosis are described. It is established that natural products from these structure classes are often biosynthesised by microorganisms. Therefore it is hypothesised that some bioactive polyketides and peptides originally isolated from plants are in fact produced by their endophytes. This is of interest for further endophyte natural product investigations., (Copyright © 2014 Elsevier GmbH. All rights reserved.)

The Title Compound (systematic Name: 3,7-dihy-droxy-9-meth-oxy-1-methyl-6H-benzo[c]chromen-6-one dimethyl sulfoxide monosolvate), C15H12O5·C2H6OS, was isolated from an unidentified endophytic fungus (belonging to class Ascomycetes) of Taxus sp. In the crystal, both the alternariol 9-O-methyl ether (AME) and the dimethyl sulfoxide (DMSO) mol-ecules exhibit crystallographic mirror symmetry. One of the hy-droxy groups makes bifurcated hydrogen bonds, viz. an intra-molecular bond with the carbonyl group and an inter-molecular bond with the carbonyl group in an inversion-related AME mol-ecule. In the crystal, the AME mol-ecules are organized into stacks parallel with the b axis by π-π inter-actions between centrosymmetrically related mol-ecules [the distance between the centroid of the central ring and the centroid of the meth-oxy-substituted benzene ring in the next mol-ecule of the stack is 3.6184 (5) Å]. Pairs of DMSO mol-ecules, linked via centrosymmetric C-H⋯O contacts, are inserted into the voids created by the AME mol-ecules, making O-H⋯O and C-H⋯O contacts with the hosts.

The bioactive compounds of medicinal plants are products of the plant itself or of endophytes living inside the plant. Endophytes isolated from eight different anticancer plants collected in Yunnan, China, were characterized by diverse 16S and 18S rRNA gene phylogenies. A functional gene-based molecular screening strategy was used to target nonribosomal peptide synthetase (NRPS) and type I polyketide synthase (PKS) genes in endophytes. Bioinformatic analysis of these biosynthetic pathways facilitated inference of the potential bioactivity of endophyte natural products, suggesting that the isolated endophytes are capable of producing a plethora of secondary metabolites. All of the endophyte culture broth extracts demonstrated antiproliferative effects in at least one test assay, either cytotoxic, antibacterial or antifungal. From the perspective of natural product discovery, this study confirms the potential for endophytes from medicinal plants to produce anticancer, antibacterial and antifungal compounds. In addition, PKS and NRPS gene screening is a valuable method for screening isolates of biosynthetic potential.

Traditional Chinese medicine encompasses a rich empirical knowledge of the use of plants for the treatment of disease. In addition, the microorganisms associated with medicinal plants are also of interest as the producers of the compounds responsible for the observed plant bioactivity. The present study has pioneered the use of genetic screening to assess the potential of endophytes to synthesize bioactive compounds, as indicated by the presence of non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) genes. The total DNA extracts of 30 traditional Chinese herbs, were screened for functional genes involved in the biosynthesis of bioactive compounds. The four PCR screens were successful in targeting four bacterial PKS, six bacterial NRPS, ten fungal PKS and three fungal NRPS gene fragments. Analysis of the detected endophyte gene fragments afforded consideration of the possible bioactivity of the natural products produced by endophytes in medicinal herbs. This investigation describes a rapid method for the initial screening of medicinal herbs and has highlighted a subset of those plants that host endophytes with biosynthetic potential. These selected plants can be the focus of more comprehensive endophyte isolation and natural product studies.

Fatty acid synthase (FAS) catalyzes the synthesis of palmitate from the sequential condensation of an acetyl primer with two carbon units added from malonyl-CoA. Inhibition of the beta-ketoacyl synthase domain of mammalian FAS leads to selective cytotoxicity to various cancer cell lines in vitro and in vivo. Also, inhibitors of FAS can cause reduced food intake and body weight in mice. Naturally occurring thiolactomycin (TLM) was used as a template to develop a new class of type I FAS inhibitors. Using a flexible synthesis, families of TLM structural analogues were obtained that possess selective FAS activity and display anticancer and weight loss effects. Compounds 13a and 13d inhibit pure FAS (ZR-75-1 breast cancer, IC(50) = 50 microg/mL), and display effective weight loss in BalbC mice (>5%). Another subclass of TLM derivatives (23b-d, 31a) exhibits FAS activity (IC(50) = 5%), and is cytotoxic to cancer cells (IC(50) < 38 microg/mL). Finally, a third subclass (16b, 29, 30) is also active against FAS (IC(50) =

This article explores how the role of the hospital nurse has been transformed by managed care, with a concentration on changes relevant to communicative relationships and processes. Two brief case analyses are considered to examine how hospital nurses have felt the impact of being on the "front lines" of managed care. Findings illustrate the utility of a communication perspective in understanding changes in nursing at individual, organizational, and system levels.

We present here the description of genes coding for molluscan hemocyanins. Two distantly related mollusks, Haliotis tuberculata and Octopus dofleini, were studied. The typical architecture of a molluscan hemocyanin subunit, which is a string of seven or eight globular functional units (FUs, designated a to h, about 50 kDa each), is reflected by the gene organization: a series of eight structurally related coding regions in Haliotis, corresponding to FU-a to FU-h, with seven highly variable linker introns of 174 to 3,198 bp length (all in phase 1). In Octopus seven coding regions (FU-a to FU-g) are found, separated by phase 1 introns varying in length from 100 bp to 910 bp. Both genes exhibit typical signal (export) sequences, and in both cases these are interrupted by an additional intron. Each gene also contains an intron between signal peptide and FU-a and in the 3' untranslated region. Of special relevance for evolutionary considerations are introns interrupting those regions that encode a discrete functional unit. We found that five of the eight FUs in Haliotis each are encoded by a single exon, whereas FU-f, FU-g, and FU-a are encoded by two, three and four exons, respectively. Similarly, in Octopus four of the FUs each correspond to an uninterrupted exon, whereas FU-b, FU-e, and FU-f each contain a single intron. Although the positioning of the introns between FUs is highly conserved in the two mollusks, the introns within FUs show no relationship either in location nor phase. It is proposed that the introns between FUs were generated as the eight-unit polypeptide evolved from a monomeric precursor, and that the internal introns have been added later. A hypothesis for evolution of the ring-like quaternary structure of molluscan hemocyanins is presented.

In contrast to small allosteric systems (like hemoglobin) those containing very large numbers (n) of binding sites never exhibit cooperativity (as measured by the Hill coefficient, nH) even approaching the potential limit, n. The reason for this appears to be that in such macromolecules the cooperative unit always represents some sub-structure of the entire structure. On the other hand, it is frequently observed that such sub-structures, when isolated, do not exhibit cooperativity at all. This paper describes studies of some molluscan hemocyanins that explore this apparent anomaly. It is concluded that it is the higher order structure of the molecule that provides a framework within which the sub-structures may exhibit their allosteric behavior.

Sequencing of the subunit of the hemocyanin of Octopus dofleini has been completed from a cDNA library. This represents the first molluscan hemocyanin to be completely sequenced. The sequence determined is for one of the two distinguishable cDNAs which have been recognized for this protein. The protein subunit has 2896 amino acids and contains seven functional units, each carrying two sets of three invariant histidine residues constituting the binding sites (A and B) for two copper atoms. The accompanying paper identifies this site in the C-terminal functional unit (Odg). Differences in sequence for the two cDNAs, for the region in which both are available, are concentrated in the "linker regions" between functional units. The sequences of the seven units exhibit high similarity, averaging about 40% identity, with a concentration of conserved sequences in the region surrounding the copper binding sites. The sequences around the B-site show significant homology to the sequences of arthropod hemocyanins. Comparison of the functional unit sequences in terms of hydrophobicity and surface exposure profiles, as well as regions of probable secondary structure, indicate that all functional units probably have a common tertiary folding; the protein subunit is a string of similarly folded beads. A number of putative N-linked carbohydrate binding sites can be recognized in the sequence; one of these corresponds to the carbohydrate observed in the X-ray diffraction study of functional unit Odg as disclosed in the accompying paper. Phylogenetic analysis of the sequences of the O. dofleini functional units, and comparison with other available molluscan sequences indicates that the multi-domain subunit structure must have arisen over a relatively brief period, preceeding the differentiation of major molluscan types.

Hemocyanins are giant oxygen transport proteins found in many arthropods and molluscs. Freely dissolved in the hemolymph, they are multisubunit proteins that contain many copies of the active site, a copper atom pair that reversibly binds oxygen. Octopus hemocyanin is composed of ten subunits, each of which contain seven oxygen-binding "functional units". The carboxyl-terminal 47 kDa functional unit, Odg, is a proteolytic isolate that binds oxygen reversibly while exhibiting slight Bohr and magnesium ion effects. In this work we present the X-ray structure determination and analysis of Odg at 2.3 A resolution. Odg has two structural domains: a largely alpha-helical copper binding domain, and a five-stranded anti-parallel beta-sandwich with the jelly roll topology found in many viruses. Six histidine residues ligate the copper atoms, one of which is involved in a thioether bridge. The results show that the hemocyanin from the mollusc and that from the arthropod have distinct tertiary folds in addition to the long recognized differences in their quaternary structures. Nonetheless, a comparison of Octopus and horseshoe crab hemocyanin reveals a similar active site, in a striking example of perhaps both convergent and divergent evolution.

Keyhole limpet hemocyanin (KLH), the large respiratory glycoprotein from the primitive gastropod mollusc, Megathura crenulata, is a potent immunogen used classically as a carrier protein for haptens and more recently in human vaccines and for immunotherapy of bladder cancer. Two KLH isoforms were identified and isolated by high-performance anion exchange chromatography. Subsequent analyses disclosed that these isoforms--designated KLH-A and KLH-B--were composed of distinct subunits that differed in primary structure, molecular weight (KLH-A was 449,000 and KLH-B was 392,000), polymerization/reassociation characteristics, and O2-binding constants (KLH-A had a P50 of 7.32 and KLH-B had a P50 of 2.46). Both subunits appear to be composed of eight oxygen binding domains, and reassociate in solution only with like subunits. These results support the concept that structural and functional heterogeneity is a common feature of molluscan hemocyanins, and provide a rational basis for studying and optimizing the immunostimulatory properties of KLH.

The carboxyl-terminal oxygen-binding unit of the polypeptide from Octopus dofleini hemocyanin has been crystallized in a form suitable for three-dimensional X-ray analysis. This proteolytic fragment has a molecular weight of 47 kDa and reversibly binds O2 while exhibiting a slight Bohr effect. Two types of crystals have been grown. Type I crystals, currently under analysis, belong to the orthorhombic space group P2(1)2(1)2(1) and have unit cell dimensions of 92.6 A x 167.4 A x 59.2 A. A composition of two protein molecules per asymmetric unit and 50% solvent content is consistent with a self-rotation function that identifies a non-crystallographic 2-fold axis of symmetry relating these molecules. Diffraction extending beyond 1.9 A Bragg spacings can be detected with synchrotron X-radiation.

Native Octopus dofleini hemocyanin appears as a hollow cylinder in the electron microscope. It is composed of 10 polypeptide subunits, each folded into seven globular oxygen-binding domains. The native structure reassociates spontaneously from subunits in the presence of Mg2+ ions. We have selectively removed the C-terminal domain and purified the resulting six-domain subunits. Although these six-domain subunits do not associate efficiently at pH 7.2, they undergo nearly complete reassociation at pH 8.0. The resulting molecule looks like the native cylindrical whole molecule but lacks the usual fivefold protrusions into the central cavity. Partially reassociated mixtures show dimers of the subunit that have a characteristic parallelogram shape when lying flat on the electron microscope grid, and a "boat" form in side view. Removal of the C-terminal domain from monomers results in the removal of two characteristically placed domains in the dimers. These observations allow the development of a model for the arrangement of the subunits within the whole molecule. The model predicts exactly the views seen in the electron microscope of both whole molecule and dimeric intermediates.

The oxygen carrier hemocyanin occurs in the blood of Scutigera coleoptrata, a uniramous arthropod, as well as the crustaceans and chelicerates. The native polymer appears to be composed of substructures having the same size and electron-dense image as those of other arthropod hemocyanins but assembled into a unique multiple and arranged in a unique configuration. The simplest explanation of these findings is that the arthropod hemocyanins have a common origin, exemplifying a derived (as opposed to primitive) character shared by each of the three living groups.

Oxygen binding by Octopus dofleini hemocyanin was examined under very nearly physiological conditions. The effects of pH, ionic composition, temperature, and aggregation were controlled so that the role each plays in modulating oxygen binding can be isolated. There is a very large effect of pH on affinity, the Bohr effect (delta log P50/delta pH = -1.7), which is the same at 10 and 20 degrees C. However, cooperativity is substantially altered over the same range of pHs at the two temperatures. The allosteric properties were examined by comparing the experimental data points to curves generated by use of the Monod-Wyman-Changeux model. A computer-fitting process was developed which allowed the individual allosteric parameters to be varied independently until the best fit could be determined. The relationship between kR and kT is responsible for the effect of pH on cooperativity. A change in the allosteric properties of the T form is primarily responsible for the differences due to temperature. Changing cation concentrations when the molecule is in the fully aggregated 51S form alters affinity without influencing cooperativity. The effect of Mg2+ is much greater than that of Na+. If the 51S decamer is dissociated to 11S monomers by removing divalent cations, oxygen binding is noncooperative. There is evidence for negative cooperativity, indicating heterogeneity of function within the subunit which contains seven oxygen binding domains. Association into decamers generates conformational change which results in a much wider range of allosteric function.

The hemocyanin-like molecule found in the blood of the most primitive bivalves (protobranchs) reversibly binds O 2 . Its respiratory properties and its sedimentation behavior are both distinctive. Although its electron-dense image looks like that of the gastropod hemocyanins, its molecular weight differs from those of all other molluscan Hcs and is more consistent with the concept of bivalve hemocyanin as a pair of octopod hemocyanins. Bivalve hemocyanin occurs in the solemyoids as well as the nuculoids, which argues for the integrity of the Protobranchia as a natural taxon. The ancestral bivalve O 2 carrier was previously believed to be a simple intracellular hemoglobin, which is found in the less primitive Pteriomorpha. The most obvious interpretation of the present results, however, is that hemocyanin is the primitive bivalve O 2 cannier and that it was replaced by the red blood cell, which originated at least twice: once in the pteriomorph bivalves and at least once in other taxa.

Employment of high-precision thin-layer methods has enabled detailed functional characterization of oxygen and carbon monoxide binding for (1) the fully assembled form with 70 binding sites and (2) the isolated chains with 7 binding sites of Octopus dofleini hemocyanin. The striking difference in the cooperativities of the two ligands for the assembled decamer is revealed through an examination of the binding capacities and the partition coefficient, determined as functions of the activities of both ligands. A global analysis of the data sets supported a two-state allosteric model assuming an allosteric unit of 7. Higher level allosteric interactions were not indicated. This contrasts to results obtained for arthropod hemocyanins. Oxygen and carbon monoxide experiments performed on the isolated subunit chain confirmed the presence of functional heterogeneity reported previously [Miller, K. (1985) Biochemistry 24, 4582-4586]. The analysis shows two types of binding sites in the ratio of 4:3.

1. The pH dependence of Octopus dofleini hemocyanin oxygenation is so great that below pH 7.0 the molecule does not become fully oxygenated, even in pure O2 at 1 atm pressure. However, the curves describing percent oxygenation as a function of PO2 appear to be gradually increasing in oxygen saturation, rather than leveling out at less than full saturation. Hill plots indicate that at pH 6.6 and below the molecule is stabilized in its low affinity conformation. Thus, the low saturation of this hemocyanin in air is due to the very large Bohr shift, and not to the disabling of one or more functionally distinct O2 binding sites on the native molecule. 2. Experiments in which pH was monitored continuously while oxygenation was manipulated in the presence of CO2 provide no evidence of O2 linked binding of CO2. While CO2 does influence O2 affinity independently of pH, its effect may be due to high levels of HCO3- and CO3-, rather than molecular CO2, and it may entail a lowering of the activities of the allosteric effectors Mg2+ and Ca2+.

The equilibria between the native (decameric) Octopus hemocyanin and its subunits were studied by analytical sedimentation. Equilibrium is obtained slowly, but the reaction is thermodynamically reversible. The mass action law for a monomer-decamer reaction is obeyed. The reassociated hemocyanin is virtually identical in its sedimentation behavior and oxygen binding with the native protein. The association-dissociation equilibria are mediated by cations; Mg2+, Ca2+, Na+, and H+ are all effective in stabilizing the decameric form at appropriate concentrations. About three to four cations per monomer must be bound for association to occur. Under some conditions, dimers of the subunits can be observed, but formation of this dimer does not depend on cation concentration, and it does not appear to be an obligate intermediate in the association to decamer.

The C-terminal domain, Od-1, of the 7-domain subunit of Octopus dofleini hemocyanin has been prepared by partial trypsinolysis followed by ion-exchange chromatography. It binds oxygen reversibly and is homogeneous in molecular weight. Its physical properties have been compared with those of the subunit. The domain molecular weight is found by sedimentation equilibrium to be 4.7 X 10(4), in excellent agreement with the result recently obtained in our laboratory from cDNA sequencing of this domain [Lang, W. H. (1988) Biochemistry (preceding paper in this issue)]. It has a sedimentation coefficient of 3.8 S. Both the molecular weight and sedimentation coefficient are consistent with the domain constituting approximately one-seventh of the Mr 3.5 X 10(5) subunit. Its amino acid composition and carbohydrate content differ significantly from that of the whole subunit, confirming the heterogeneity in domains previously established on an immunological basis. Circular dichroism predicts similar secondary structure for the domain and subunit. The domain does not self-associate in the presence of Mg2+ but does bind to the whole molecule in a ratio of approximately 1 domain/subunit. The oxygen affinity of this domain is quite low. It shows intrinsic magnesium and Bohr effects similar to those of the whole molecule but of greatly reduced magnitude.