Chemical and immunological characterization of a unique antigenic region in lysozyme.
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Biomedical subjects
Publications and source records attributed to R Arnon.
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A synthetic peptide consisting of the aminoacid sequence of residues 64-82 of lysozyme, with alanine replacing cysteine as residue 76, was prepared by the solid-phase technique. Mild reduction followed by reoxidation in air of the deprotected peptide led to the formation of a closed loop containing an intrachain disulfide bond. A conjugate consisting of this "loop" attached to multi-poly(DL-alanyl)-poly(L-lysine) elicited, in rabbits and goats, the formation of antibodies capable of reacting with lysozyme and with the loop peptide prepared from it. These immunological interactions can be inhibited by either lysozyme or the loop peptide, but not by the performic acid-oxidized open-chain peptide. Thus, the antibodies elicited by the completely synthetic antigen show specificity toward the "loop" structure (residues 64-80) of native lysozyme.
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A synthetic conjugate, prepared by covalent binding of a lysozyme fragment (sequence 64-83, denoted "loop" peptide) to a synthetic branched polypeptide, elicited in rabbits the formation of antibodies with specificity directed against a unique region in native lysozyme. These anti-"loop" antibodies were isolated immunospecifically on a lysozyme-cellulose immunoadsorbent. Antibodies with a similar specificity were isolated from antilysozyme sera with an immunoadsorbent prepared from the same "loop" peptide. The capacity of the anti-"loop" antibodies to distinguish between the "loop" peptide, containing a disulfide bridge, and the open-chain peptide derived from it suggests that they are directed against a conformation-dependent determinant.
Antibodies were prepared in rabbits against trypsins obtained from four different species-namely bovine, porcine, spiny Pacific dogfish, and starfish (Evasterias trochelii). Each of the antisera, or the immunoglobulin G fraction thereof, was tested for its capacity to react with each of the four enzymes. The immunological reaction was assessed by three different techniques-precipitin reaction, antigen binding capacity, and inhibitory effect of the antibodies on the proteolytic activity of the enzymes. In each case, the homologous enzyme gave the strongest reaction with its antiserum but the heterologous enzymes were also capable of reacting to an appreciable extent. The cross-precipitation was the least sensitive method, and gave relatively low values, whereas cross-inhibition and cross-binding of radioactively labeled antigens indicated high extent of cross-reaction between the various trypsins. The relative capacity of interaction of the four enzymes with the four antibodies could be related to the order in which these enzymes developed during evolution. Thus the "order" of similarity was bovine > porcine > dogfish > starfish.
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