Classification of sheep abomasal mucosal mast cell proteinase as a serine endopeptidase (EC 3.4.21)

1. Diisopropylphosphofluoridate (Dip-F) and phenylmethanesulphonylfluoride (Pms-F) are inhibitors of "serine" proteinases, and L-trans-epoxysuccinylleucylamido-(4-guanido)-butane (E-64) is an inhibitor of "thiol" proteinases. The effects of these inhibitors on sheep mast cell proteinase (SMCP) were examined. 2. Enzyme activity was completely inhibited by 5 mM Dip-F following a 4-hr preincubation period at either 4 degrees C or 30 degrees C but was unusually resistant to the action of 1 mM Dip-F. 3. SMCP activity was inhibited by 1 mM Pms-F at both 4 degrees C and 30 degrees C. Inhibition was reversed by dithiothreitol (DTT), but this effect was virtually eliminated following preincubation with Pms-F at 30 degrees C for 12 hr. 4. SMCP activity was unaffected by E-64. 5. These properties are consistent with the classification of SMCP as a "serine" endopeptidase (EC 3.4.21).