Methionyl Bonds Research Articles

Biological activity of the cleavage product of human immunoglobulin G with cyanogen bromide.

Treatment of human IgG with cyanogen bromide in 0.05 M HCl under specified conditions resulted in the cleavage of about half of its methionyl peptide bonds. A major fragment of about 5S was isolated from the reaction mixture by gel filtration in quantitative yield. The CNBr fragment reacted fully with goat antiserum against human light chain, but its reaction with anti-heavy chain was markedly decreased. The treatment with CNBr caused a drastic decrease in the following biological activities of IgG: complement fixing, skin binding, reaction with antiglobulin factors, and reaction with specific anti-Gm(12) serum. On the other hand, the reaction with serum of anti-Gm(1) or anti-Gm(4) specificity was not impaired and antibody activity, namely antistreptolysin and isohemagglutinin, was retained after the treatment with CNBr. It is concluded that the CNBr cleaves preferentially the methionyl bonds in the Fc portion of IgG, and that the major fragment obtained, denoted F(ab'')(2), has still the combining properties of a divalent antibody. The possible therapeutic uses of F(ab'')(2) are discussed.

Sequence of thirteen amino acids in the C-terminal end of bovine growth hormone and localization of a disulflde bridge

The carbamidomethyl derivative of reduced bovine growth hormone (BGH) was extensively attacked by carboxypeptidases A and B, and approximately 19 moles of various amino acids was liberated. The correct sequence of 13 amino acids could be established by selective cleavage of the methionyl bonds in the molecule and isolation of a C-terminal dodecapeptide by filtration through Sephadex G-25. The structure of this peptide was studied by carboxypeptidase A attack, Edman degradation, and further study of the fragments obtained by chymotryptic digestion. A disulfide bond connecting the two half-cystines in the dodecapeptide was discovered by the comparative study of the peptides released by the action of cyanogen bromide on native or reduced and blocked hormone. The structure of the C-terminal end in BGH is: ▪

Cleavage with cyanogen bromide of methionyl bonds in collagen

Cleavage with cyanogen bromide of methionyl bonds in collagen

Progress in non-enzymatic selective modification and cleavage of proteins

Publisher Summary This chapter discusses the progress in nonenzymatic selective modification and cleavage of proteins. Cyanogen bromide cleaves methionyl bonds in acidic medium in high yields with practically no side reactions. Cleavage of the four methionyl bonds in ribonuclease proceeds in yields up to 85–95%. Gel filtration permits the isolation of an N-terminal 13-unit peptide, free homoserine, and the core. Cyanogen bromide cleavage of sperm whale myoglobin, containing two methionine residues, followed by gel filtration on Sephadex GS-25 and GS-75, has led to the isolation of three peptides in high yield. N-bromosuccinimide and N-bromoacetamide can be used for the selective cleavage of C-tryptophyl and C-tyrosyl bonds and for the selective oxidation of indole to oxindole residues. Tryptophan residues of chymotrypsin are more accessible to oxidation than in di-isopropyl-phosphoryl-chymotrypsin. The difference spectrum of DIP-chymotrypsin (one tryptophan oxidized) versus chymotrypsin (one tryptophan oxidized) is identical with the difference spectrum of DIP-chymotrypsin versus chymotrypsin.