Arginine residue, side-chain hydrolysis

For example, chymotrypsin cleaves peptides on the C-terminal side of aromatic amino acid residues phenylalanine, tyrosine, and tryptophan, and to a lesser extent some other residues with bulky side-chains, e.g. Leu, Met, Asn, Gin. On the other hand, trypsin cleaves peptides on the C-terminal side of the basic residues arginine and lysine. Elastase usually catalyses hydrolysis of peptide bonds on the C-terminal side of neutral aliphatic amino acids, especially glycine or alanine. These three pancreatic enzymes are about 40% identical in their amino acid sequences, and their catalytic mechanisms are nearly identical. 

Presently, FAB-MS spectra are routinely used to characterize synthetic tyrosine O-sulfate peptides.152,57,63-671 Since partial hydrolysis of the sulfate ester occurs in the gas phase, quantification of the tyrosine O-sulfate residue by mass spectrometry is not possible, but combined with one-peak assignment in HPLC, FAB-MS represents a powerful analytical tool. On the other hand, partial hydrolysis in the gas phase excludes the presence of sul-fonated species which should be perfectly stable. In early studies the presence of such species were excluded by quantitative recovery of tyrosine upon acid hydrolysis or upon hydrolysis with arylsulfatase.1361 Recently, even MALDI-TOF-MS spectra of CCK-peptides1441 and of conotoxins a-PnIA and a-PnlB 138 were reported which show that in the positive-ion mode the [M + H-S03]+ ions represent the base peaks, while in the negative-ion mode, [M-H]-ions consistently correspond to the base peaks. In the CCK peptides intramolecular salt bridging of the sulfate hemi-ester with proximal positive charges of arginine or lysine side chains was found to reduce the extent of hydrolysis in the gas phase significantly.144,1491... 

Trypsin, chymotrypsin, and elastase—three members of the serine protease family—catalyze the hydrolysis of proteins at internal peptide bonds adjacent to different types of amino acids. Trypsin prefers lysine or arginine residues chymotrypsin, aromatic side chains and elastase, small, nonpolar residues. Carboxypeptidases A and B, which are not serine proteases, cut the peptide bond at the carboxyl-terminal end of the chain. Carboxypeptidase A preferentially removes aromatic residues carboxypeptidase B, basic residues. (Illustration copyright by Irving Geis. Reprinted by permission.)... 

The rate of hydrolysis is affected by the amino acid that follows the basic residue in the sequence. Thus the Arg-Asp bond is cleaved more slowly than most other peptide bonds on the right side of arginine. Similarly, the bond between arginine and cysteic acid (the oxidized form of cysteine) is relatively resistant to tryptic hydrolysis. As it will be shown later such differences can be exploited in sequence studies, but it is possible to create even more substantial differences by appropriate modifications of the peptide molecule. For instance, treatment of a peptide that contains both lysine and arginine residues with maleic acid anhydride or preferably with citraconic acid anhydride yields derivatives in which the lysine residues have no free amino group in their side chain... 

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