Isolation and amino-terminal sequence analysis of two dissimilar pancreatic proelastases from the african lungfish, protopterus aethiopicus

Two proelastases, A and B, having molecular weights of about 25,000, were isolated in highly purified form from the pancreata of the African lungfish, Protopterus aethiopicus. Activation with trypsin yielded active enzymes having typical elastase specificity. These enzymes digested elastin and hydrolyzed the specific ester substrate Ac-(Ala)₃- OMe, but not Ac-Tyr-OEt or Tos-Arg-OMe. The elastolytic activity of elastase B and the affinity of the enzyme for Ac- (Ala)s-OMe were higher than those of elastase A and resembled those of porcine elastase. Sequence analysis of proelastase A demonstrated that the “activation peptide” is very similar to that of the chymotrypsinogen family, especially that of chymotrypsinogen C. Amino-terminal sequence analysis of elastase A revealed a closer relationship to the chymotrypsinogen family, especially chymotrypsinogen C, than to either porcine elastase or lungfish elastase B. The sequence of the “activation peptide” of proelastase B had no obvious relationship to that of the zymogens of the other pancreatic serine proteases. The amino-terminal sequence of elastase B, however, resembles that of porcine elastase more closely than that of chymotrypsin, trypsin, or elastase A.