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Disruption of the coat of coated vesicles is accompanied by the release of clathrin and other proteins in soluble form. The ability of solubilized coated vesicle proteins to reassemble into empty coats is influenced by Mg2+, Tris ion concentration, pH, and ionic strength. The proteins solubilized by 2 M urea spontaneously reassemble into empty coats following dialysis into isolation buffer (0.1 M MES--1 m M EGTA--1 mM MgCl2--0.02% NaN3, pH 6.8). Such reassembled coats have sedimentation properties similar to untreated coated vesicles. Clathrin is the predominant protein of reassembled coats; most of the other proteins present in native coated vesicles are absent. We have found that Mg2+ is important in the coat assembly reaction. At pH 8 in 0.01 M or 0.1 M Tris, coats dissociate; however, 10 mM MgCl2 prevents dissociation. If the coats are first dissociated at pH 8 and then the MgCl2 is raised to 10 mM, reassembly occurs. The results suggest that Mg2+ stabilizes the coat lattice and promotes reassembly. This hypothesis is supported by our observations that increasing Mg2+ (10 microM--10 mM) increases reassembly whereas chelation of Mg2+ by (EGTA) inhibits reassembly. Coats reassembled in low-Tris (0.01 M, pH 8) supernatants containing 10 mM MgCl2 do not sediment, but upon dialysis into isolation buffer (pH 6.8), these coats become sedimentable. Nonsedimentable coats are noted also either when partially purified clathrin (peak I from Sepharose CL4B columns) is dialyzed into low-ionic-strength buffer or when peaks I and II are dialyzed into isolation buffer. Such nonsedimentable coats may represent intermediates in the assembly reaction which have normal morphology but lack some of the physical properties of native coats. We present a model suggesting that tightly intertwined antiparallel clathrin dimers form the edges of the coat lattice.

Coated vesicles were purified and characterized from porcine brain and chicken oocyte. Electrophoresis on sodium dodecylsulphate (SDS) gels showed that coated vesicles from either source have three major proteins in common with apparent molecular weights of 180000, 120000, and 55000 Daltons. Negatively stained specimens from both sources appear to consist of a highly ordered array of short interconnected rods or ridges of material on the exterior surface of a membrane vesicle. Coated vesicles purified from porcine brain and chicken oocyte have mean external diameters of 75.0 and 85.0 nm, respectively. In coated vesicles of the appropriate orientation, portions of the coat material appear to be organized into hexagons and pentagons. Based on the observed variability of size and apparent structure, it is postulated that the basic structural subunits of coated vesicles are the short rods or ridges of material observed on the exterior membrane vesicle surface. It is suggested that multiples of the subunits can be assembled into many arrangements to yield coated vesicles of different sizes and coat structure. It is also proposed that the structural subunit is a complex of 3 proteins of molecular weight of 180000, 120000 and 55000 Daltons.

A panel of monoclonal antibodies was raised against human serum albumin from fusions of BALB/c splenocytes and SP2/0-Ag14 murine myeloma cells. This panel was screened against purified albumins from 21 species including chimpanzee, gorilla, and orangutan. A monoclonal antibody (HSA-1) specific for human albumin was identified. The epitope recognized by HSA-1 was shown to be conserved in all human blood samples tested. A double antibody ELISA assay was developed using biotinylated HSA-1 as the specific probe for human albumin. This assay was capable of detecting as little as 30 nanograms or less albumin/ml. This assay was used to verify the presence of human albumin in blood, tissue extracts, and other body fluids. These results show that the HSA-1 monoclonal antibody can be used in determining the human origin of blood, tissue, and a variety of other body fluids.

Two carbohydrate-binding probes, the lectin concanavalin A and an anti-carbohydrate monoclonal antibody designated FMG-1, have been used to study the distribution of their respective epitopes on the surface of Chlamydomonas reinhardtii, strain pf-18. Both of these ligands bind uniformly to the external surface of the flagellar membrane and the general cell body plasma membrane, although the labeling is more intense on the flagellar membrane. In addition, both ligands cross-react with cell wall glycoproteins. With respect to the flagellar membrane, both concanavalin A and the FMG-1 monoclonal antibody bind preferentially to the principal high molecular weight glycoproteins migrating with an apparent molecular weight of 350,000 although there is, in addition, cross-reactivity with a number of minor glycoproteins. Western blots of V-8 protease digests of the high molecular weight flagellar glycoproteins indicate that the epitopes recognized by the lectin and the antibody are both repeated multiple times within the glycoproteins and occur together, although the lectin and the antibody do not compete for the same binding sites. Incubation of live cells with the monoclonal antibody or lectin at 4 degrees C results in a uniform labeling of the flagellar surface; upon warming of the cells, these ligands are redistributed along the flagellar surface in a characteristic manner. All of the flagellar surface-bound antibody or lectin collects into a single aggregate at the tip of each flagellum; this aggregate subsequently migrates to the base of the flagellum, where it is shed into the medium. The rate of redistribution is temperature dependent and the glycoproteins recognized by these ligands co-redistribute with the lectin or monoclonal antibody. This dynamic flagellar surface phenomenon bears a striking resemblance to the capping phenomenon that has been described in numerous mammalian cell types. However, it occurs on a structure (the flagellum) that lacks most of the cytoskeletal components generally associated with capping in other systems. The FMG-1 monoclonal antibody inhibits flagellar surface motility visualized as the rapid, bidirectional translocation of polystyrene microspheres.

Sodium dodecyl sulfate/polyacrylamide gels of coated vesicles from porcine brain (mean 76% coated vesicles) show three major proteins (180,000, 125,000, and 55,000 daltons) that account for 73% of the total protein. Preparations consisting predominantly of coats (65%) have less of the 55,000-dalton protein. Clathrin (180,000 daltons) comprises 40% of the protein of a coated vesicle. Conditions of 2 M urea, 0.25 M MgCl2, or pH 7.5 disrupt the coat and solubilize clathrin. Solubilized clathrin reforms coat structures after dilution of urea or MgCl2. High-pH-solubilized clathrin reassembles after dialysis against buffer at pH 6.5 containing dithiothreitol (5 mM). Reassembled coats are predominantly clathrin.

Monoclonal antibody mouse antihuman semen-5 (MHS-5) (immunoglobulin G1 [IgG1]) was biotinylated using N-biotinyl-w-aminocaproic acid-N-hydroxysuccinimide ester. This monoclonal antibody-biotin conjugate recognized low molecular weight peptide bands between 10.5 and 20 kilodaltons on immunoblots of liquefied semen. Immunodominant peptides had molecular weights of 10.5, 11.5, and 13.5 kilodaltons. An enzyme-linked immunosorbent assay (ELISA) developed with the biotinylated-MAb and streptavidin peroxidase demonstrated sensitivity curves with lower limits of 10 ng of seminal fluid protein per microtiter well using 50 ng per well of monoclonal antibody-biotin conjugate. Cross-reactivity studies on a panel of human biological fluids and tissues demonstrated no cross-reactivity or false positives using the monoclonal antibody-biotin conjugate. The sensitivity of the monoclonal antibody-biotin ELISA was compared to ELISA based upon a polyclonal secondary antibody-peroxidase conjugate. These findings indicate that this ELISA assay, based on a biotinylated monoclonal antibody to a seminal vesicle-specific antigen, may be useful for semen identification.