The third serine proteinase with chymotrypsin specificity isolated from Atlantic cod (Gadus morhua) is a type‐II elastase

Preparations of chymotrypsin from Atlantic cod are heterogeneous and previously gave rise to two active peaks when subjected to pH‐gradient chromatography. Extension of the pH‐gradient resolved a third protein peak with benzoyltyrosine ethylester hydrolytic activity. The first two peaks have been characterized as chymotrypsin variants and designated A and B, whereas the identity of the third peak was not clear. Analysis of this protein by Edman sequencing and mass spectrometry has now confirmed a high degree of identity with the predicted protein sequence from a recently described cDNA clone. That sequence was named elastase B by sequence comparison. As the present elastase deviates in 16 positions from that of elastase B, we have named it elastase C. The elastase C was active in hydrolysing typical substrates used by chymotrypsin, namely benzoyl‐ L‐tyrosine ethylester and succinyl‐Ala‐Ala‐Pro‐Phe‐p‐nitroanilide, but inactive against the typical elastase substrates succinyl‐Ala‐Ala‐Ala‐p‐nitroanilide and orcein‐elastin. Comparison of the kinetic properties of the cod elastase C with bovine chymotrypsin and cod chymotrypsin variants A and B, using succinyl‐Ala‐Ala‐Pro‐Phe‐p‐nitroanilide, showed a lower catalytic efficiency of elastase C. The effects of several inhibitors on cod elastase C were identical to effects on chymotrypsins variants A and B, but dissimilar when compared with porcine pancreatic elastase. On the basis of the specificity and amino acid sequence, we conclude that the enzyme under study is most correctly classified as a type‐II elastase.