Abstract
1.5 g of a weakly cationic chymotrypsinogen (chymotrypsinogen A) and 5 g of trypsinogen can be obtained in essentially homogeneous form from 1 kg of fresh pig pancreas by a single chromatographic step on CM-cellulose. The molecular weight of the porcine chymotrypsinogen A is between 24 000 and 25 000 as determined by ultracentrifugation and by filtration through Sephadex G-100. The amino acid composition resembles those of bovine chymotrypsinogens A and B rather than that of porcine chymotrypsinogen C. Porcine chymotrypsinogen A and bovine chymotrypsinogens A and B contain the same number of histidines (2), tryptophans (8) and disulfide bridges (5), but porcine chymotrypsinogen A contains 5 tyrosines (instead of 4 in bovine A and 3 in bovine B), 2 methionines as in bovine A (compared with 4 in bovine B) and 16 prolines (compared with 9 in bovine A). The N-terminal sequence (first 17 residues) of porcine chymotrypsinogen A and bovine chymotrypsinogens A and B are the same with two exceptions: glutamine at position 7 of bovine chymotrypsinogens A and B is replaced by proline in the porcine chymotrypsinogen and serine at position 14 in porcine chymotrypsinogen A and bovine chymotrypsinogen A is replaced by alanine in bovine chymotrypsinogen B. The arrangement of the 16 residues in the vicinity of the “histidine loop” is identical with that already found by others in bovine chymotrypsinogens A and B. The three chymotrypsinogens studied so far are activated by the cleavage of the Arg 15Ile 16 bond. However, porcine chymotrypsin A π and bovine chymotrypsin B π, in contrast with bovine chymotrypsin A π, do not autolyze and, consequently, do not form a chymotrypsin δ.
Published Version
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