Purification and properties of a pepstatin-insensitive carboxyl proteinase from a gram-negative bacterium

A carboxyl proteinase was found in the culture filtrate of a Gram-negative bacterium. The optimum for the action of the purified enzyme was approx. pH 3 and its caseinolytic activity was not inhibited by carboxyl proteinase inhibitors, such as pepstatin, Streptomyces pepsin inhibitor and diazoacetyl-DL-norleucine methyl ester. 1,2-epoxy-3-(p-nitrophenoxy)propane modified the enzyme with concomitant loss of its enzyme activity. The enzymatic and physicochemical properties of the enzyme were compared with those of known pepstatin- and diazoacetyl-DL-norleucine methyl ester-insensitive carboxyl proteinases previously reported. To our knowledge, this is the first carboxyl proteinase isolated from bacteria.