IDENTIFICATION OF HISTIDINE IN ACTIVE CENTER OF CHYMOTRYPSINS FROM A REPTILE AND A FISH

Chymotrypsin preparations from pancreactic tissue of two lower vertebrates, the turtle Pseudemys elegans and the teleost fish Thunnus secundodorsalis, were reacted with [carbonyl-14C] tosyl-l-phenylalanine chloromethyl ketone. The alkylated protein was oxidized and hydrolyzed, and the labeled products were identified and measured in the effluent of an amino acid analysis chromatographic system. The results show that this inhibitor, which is known to selectively alkylate histidine-57 of bovine chymotrypsin A at N-3, alkylates in each of these species also only one histidine residue at N-3. From this and other evidence, it is concluded that the active center of chymotrypsins is basically identical in structure throughout the vertebrates from the fish to the mammals. © 1969.