Microheterogeneity in porcine pancreatic amylase preparations due to disulfide-sulfhydryl exchange

Abstract

There are two masked SH groups in pancreatic amylase (EC 3.2.1.1) which become reactive after removal of Ca ions, and then only due to fluctuation of the polypeptide chain. Carboxymethylation of the masked SH groups and isolation of the tryptic CM-peptides have shown that the reacting SH groups in active amylase preparations are not identical, depending on the method of preparation. The microheterogeneity is attributed to an SH-SS exchange reaction taking place during preparation. This exchange results in a mixture of two types of amylase molecules containing different SH groups. The tryptic peptides containing the SH groups have been detected from the r radioautogram of the peptide map of the [ 14C] carboxymethylated protein digest. We identified the SH peptides present in native amylase, and those cysteinyl peptides which form an wasily reducible disulfide in the vicinity of these thiol groups, and take part in the intramolecular SH-disulfide exchange.