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Pheophytinization of bacteriochlorophyll (BChl) at low pH was investigated in the core (LH1) and peripheral (LH2) light-harvesting complexes, as well as in the ensemble of the reaction center (RC) with the LH1 complex. The stages in disintegration of the native BChl forms in the LH1 complex and in its ensemble with RC were revealed. They were observed as emergence of the absorption band of monomeric BChl and an increase in its intensity, followed by its transformation into the band of monomeric bacteriopheophytin (BPh) and then into the band of aggregated BPh. Unlike the LH1 complex, in the case of the LH2 complex monomeric BChl was never detected as an intermediate product. While the spectra revealed formation of monomeric BPh, its accumulation did not occur, since its aggregation is very rapid compared to that in the LH1 complex and in the RC-LH1 ensemble. PAG electrophoresis revealed that pheophytinization of BChl in the LH2 complex was accompanied by disruption of the stable cylindrical structure of this complex with emergence of characteristic fragments consisting of α and β peptides and bearing monomeric BPh, as well as of the α peptide aggregates bearing BPh aggregates. Unlike the LH2 complex, BChl pheophytinization in the LH1 complex did not result in its fragmentation. This is an indication of different types of structural stabilization in the LH1 and LH2 complexes. In the LH2 complex, coordination of bacteriochlorophyll Mg2+ by conservative histidine residues of the α and β polypeptides is the main factor responsible for the maintenance of its cylindrical structure. Stability of the LH1 complex is probably based primarily on the highly specific hydrophobic interactions between the surfaces of individual polypeptide chains, since the presence of hydrogen bonds results in autonomy of each αβ3BChl2 subunit, rather than in stabilization of the LH1 complex as a whole.

The review deals with the properties of astacin family of zinc-dependent metalloproteinases. One of the remarkable features of these enzymes is their ability to cleave peptidyl-arylamides, which is not typical to other metalloproteinases. Special attention is paid to physiological functions of the astacins and to the influence of domain composition and posttranslational modifications on the activity and stability of these enzymes.

Alkyl-substituted hydroxybenzenes (AHBs), auto-inducers of microbial dormancy (or d1 factors), were found to stabilize the structure of protein macromolecules, making them metabolically less active and more resistant to stresses. In vitro experiments with the Bacillus intermedius ribonuclease and chymotrypsin showed that the degree of the physical and chemical stability of these enzymes treated with AHBs depends on their concentration and incubation time. Experiments with RNase, which is capable of refolding, i.e., renaturation after heat denaturation, revealed that AHBs efficiently interact with both intact and denatured proteins. The data obtained allow the inference to be made that d1 factors may play the role of natural chemical chaperons, blocking metabolism in dormant cells through the formation of catalytically inactive thermostable complexes with enzymes.

Two novel strains i.e. Streptomyces cremeus 510 and Streptomyces litmocidini 447 producing L-glutamate oxidase were isolated from soil samples and identified. Mathematical design of the experiments made it possible to optimize the fermentation medium composition which provided at least a 5-fold increase of the strain L-glutamate oxidase activity by comparison with the initial activity in the standard medium.

A comparative study of thermostability and amino acid composition of phenylalanyl-tRNA synthetases from E. coli and Thermus thermophilus HB8 has been carried out. In the thermophilic protein the proline, leucine, phenylalanine, arginine content was considerably increased, whereas that of asparagine, isoleucine, serine, threonine and lysine was decreased as compared to the mesophilic protein. Using tritium topography, Pro, (Leu + Ile) and Gly were found to be the most accessible on the surfaces of the both enzymes. In the E. coli enzyme the threonine residues were also easy to access, while on the surface of the thermophilic enzyme arginine residues were more abundant. A quantitative assay of the surface compositions revealed the increased exposure of (Leu + Ile) residues in the thermophilic protein as well as of the charged asparagine and arginine residues. A possible relationship of the observed effects to thermostability is discussed.

The hexokinase interaction with mitochondrial membranes in rat sarcoma M-1 cells was studied. The conditions of formation of the enzyme complex with mitochondrial membranes and its stability were elaborated. The kinetic parameters of free and membrane-bound hexokinases were determined. The data obtained are discussed within the frame-work of the adsorption mechanism of hexokinase activity regulation in neoplastic tissues.

A procedure for obtaining tissue kallikrein (EC 3.4.21.35) from large specimens of human urea (100 l) has been developed. The isolation procedure included primary extraction of the protein with chitosan (a crustacean chitin deacylated by alkaline treatment), desorption from chitosan with 1 M NH3, affinity chromatography on contrical-Sepharose, ion-exchange chromatography on DEAE-Sepharose and gel filtration on Sephadex G-100. This method permits to obtain tissue kallikrein preparations purified 1080-fold (with respect to AcPheArg-OEt esterase) and 1360-fold (with respect to kininogenase) with 33 and 40% yields, respectively. Tissue kallikrein preparations were homogeneous as could be judged from the results of electrophoresis performed in 12% PAAG in the presence of 0.1% SDS as well as from the presence of one N-terminal amino acid identified as isoleucine. Purified tissue kallikrein had specific activities of 133 mumol/min/mg protein (with respect to AcPheArg-OEt hydrolysis) and 8.8 mumol/min/mg protein (with respect to D-Val-Leu-Arg-pNa hydrolysis) and liberated 462 micrograms equiv. of bradykinin/min/mg protein from heated human blood plasma used as a kininogen source. The protein exhibited the highest stability at pH 8.0-9.0; the pH optimum is at pH 8.0 with AcPheArg-OMe as substrate. The enzyme revealed a high thermostability and was fully inactivated only after 1-hour heating in a boiling water bath. The identity of the urine enzyme to tissue kallikrein could be confirmed by the resistance of the enzyme activity to SIT, high sensitivity to the inhibiting effect of aprotinin (Ki = 0.94 x 10(-10) M) and by an exceedingly low value of the second order inhibition constant for DPP (4.6 M-1 min-1). The fact that this value differs drastically from that for human blood plasma kallikrein (EC 3.4.21.34) which is equal to 360 M-1 min-1 points to marked differences in the structure of the active centers of the both kallikreins as well as to the uniqueness of the tissue kallikrein active center.

The effect of specific inductors at different stages of Streptomyces recifensis var. lyticus 2435 cultivation was studied. It is shown that introduction of killed bacterial cells into inoculum not only influences the level of accumulation of lytic enzymes by the strain S. recifensis var. lyticus 2435 but also determines the qualitative composition of the synthesized complex. The yield of bacteriological glycosidases grows with introduction of the Micrococcus lysodeikticus cells into the inoculum or of dissolvable chitin into the enzymic medium. The possibility to preserve the initial level of the lytic activity in the producer during re-inoculations by introducing the Bacillus subtilis cells into the cultivation medium has been studied.