The AFP receptor (rAFP) was discovered in embryonal and tumor tissues with a high level of proliferation. The AFP‐binding protein (AFPbp) possibly containing the AFP‐receptor (rAFP) was isolated from human embryos and human breast cancer tissue using affinity chromatography on an AFP‐Sepharose column. The similarity of molecular weight, subunit composition, and immunological characteristics was shown for embryonal and tumor AFPbp using immunoblotting, gel‐filtration, and PAAG electrophoresis. Judging from Superose‐12 gel‐filtration data, the protein molecular weight made up to 320‐380 kDa. The presence of an IgG‐binding site was detected in embryonal and tumor AFPbp by Western blot analysis.

It has been found that staphylococcal enterotoxin B contains a proteolysis-sensitive sequence in the cysteine loop formed by two half-cystines located in the middle of the toxin polypeptide chain. Fragments of the enterotoxin formed as a result of its digestion in this region have been isolated, their N-terminal scyuences have been determined and sites of proteolysis have been identified. It has been demonstrated that the N-terminal fragment of staphylococcal enterotoxin B is capable of activating T cell proliferation in the culture of human mononuclear cells practically to the same degree as the intact enterotoxin. The toxin's C-terminal fragment possesses an ability to activate calmodulindependent enzymes and is probably the toxicogenic part of the enterotoxin.Staphylococcal enterotoxins (S. enterotoxins) represent a group of proteins with molecular masses ranging between 27 -30 kDa which are secreted by Staphylococcus aureus and cause food poisoning [l]. At present, sevcn S. enterotoxins are known, namely A, B. C1, C2, C3, D and E [2]. Their amino acid sequences have been determined [3] and it was shown that all are single-chain polypeptides containing one disulfide bond formed by two half-cystines located in the middle of the polypeptide chain which form the so-called cysteine loop. S. enterotoxins are known to be most potent T cell mitogens [4]. T cell activation accompanied by induction of interleukin 2 and interferon [5] is conditioned by high-affinity interaction of S. enterotoxins with class 11 main histocompatibility complex (MHC) molecules [6] and subsequent presentation of the complex formed to a variable region of the subunit of the T cell receptor (V,TCR) [7]. From the character of receptor interactions and the nature of T cell proliferative response, the mechanism of S. enterotoxins' action on cells of the immune system is completely identical to that of MIS antigens [8, 91; on this basis, the foregoing proteins were united in the family of the so-called 'superantigens'. Despite the fact that interaction of S. enterotoxins with immunocompetent cclls has been studied in sufficient detail, there are no precise data explaining the interrelationship between immunomodulatory properties and the possible role of these toxins in pathogenesis of staphylococcal infections. There are also no data about the structural and functional organization of S. cnterotoxins and the regions of their moelcules responsible for receptor interactions and toxicogenic functions. .I).The present work is devoted to the study of the domain structure of S. enterotoxin B. We have found that it can be easily digested in the cysteine loop by contaminating proteases that are present in the toxin preparation. The fragments formed were isolated and their N-terminal amino acid sequences were determined, which allowed these fragments to be identified in the S . enterotoxin B structure. Studying the functional properties of the fragments obtained also allowed us to identify a region in the S. enterotoxin B structure that is responsible...

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SummaryThe transferrin receptor (TFR) has been detected in tissues eharacterised by a high degree of proliferation. We have developed a procedure for isolating TFR from human placental tissues by affinity chromatography on transferrinSepharose. Using gel filtration and electrophoresis in 7% PAAG, it has been shown that the molecular mass of the protein is 180 kDa. The protein has a subunit structure and is made up of two identical subunits, 90 kDa each. The constant for the protein binding to transferrin is equal to 5 x 10 .9 M. The yield of the protein isolated by the novel procedure exceeds 5-fold that obtained by previously described methods.

A panel of ten monoclonal antibodies to aflatoxins B1, B2, and G2 was produced and comprehensively characterized. The affinity and cross reactivity of these antibodies were determined using the methods of direct, indirect, and competitive ELISA. The structures of monoclonal antibody genes were comprehensively studied and the variable and constant domains of the antibody genes were cloned and sequenced. Sequencing analysis confirmed the results of isotyping the light and heavy antibody chains obtained by ELISA. Variable and constant fragments of the antibody genes were cloned into a bicistron expression vector for the recombinant Fab' fragment for one of the antibodies expressed in Escherichia coli and purified. Thus, data were obtained that can be useful for the development of an aflatoxin detection system on the basis of the described monoclonal antibodies and the creation of recombinant antibodies with changed parameters of specificity using protein engineering methods.