Autolysis of bovine enteropeptidase heavy chain: evidence of fragment 118-465 involvement in trypsinogen activation

Variations in bovine enteropeptidase (EP) activity were shown to result fro m autolysis caused by the loss of calcium ions; the cleavage sites were det ermined. The native enzyme preferred its natural substrate, trypsinogen (K- M = 2.4 mu M), to the peptide and fusion protein substrates (K-M = 200 and 125 mu M, respectively). On the other hand, the truncated enzyme composed o f the C-terminal fragment 466-800 of EP heavy chain and intact light chain did not distinguish these substrates. The results suggest that the N-termin al fragment 118-465 of the enteropeptidase heavy chain contains a secondary substrate-binding site that interacts directly, with trypsinogen. (C) 1999 Federation of European Biochemical Societies.