The differentiation of the chloroform, peptone and antigen-antibody inducible esterase activities of human serum from plasmin.

A comparative study which differentiates the chloroform inducible esterase activity of human serum from plasmin is presented. Although both esterase activities have a similar pH optimum against p-toluene sulfonyl L-arginine methyl ester, they differ in, at least, six other respects. The proenzyme of the chloroform inducible esterase activity is destroyed by heating at 56° for 30 minutes or by reducing the pH to 2.3, whereas plasminogen is stable to such treatment. The chloroform inducible esterase activity is resistant to soybean trypsin inhibitor while plasmin is mostly inhibited. Activity against N-acetyl L-tyrosine ethyl ester is induced by chloroform, but plasmin is inactive against this substrate. On the other hand, plasmin splits casein but the chloroform preparation does not. Pretreatment of serum with an antigen-antibody precipitate greatly diminishes the chloroform inducible esterase activity but not the streptokinase inducible activity. Evidence is presented which suggests that the chloroform inducible esterase activity consists of two components: one is predominantly active against p-toluene sulfonyl L-arginine methyl ester and is probably not affected by the immune precipitate; the other is more active against N-acetyl L-tyrosine ethyl ester than against p-toluene sulfonyl L-arginine methyl ester, is removed by exposing serum to immune precipitate and bears a significant resemblance to the activated first component of complement. Peptone inducible esterase activity, like that induced by chloroform, arises from a heat and acid labile precursor, is active against p-toluene sulfonyl L-arginine methyl ester and N-acetyl L-tyrosine ethyl ester, is not inhibited by soybean trypsin inhibitor, does not digest casein and is partially removed by exposing serum to the immune precipitate before peptone activation. The esterase activity taken up from serum by the immune precipitate, like that induced by chloroform or peptone, arises from a heat labile precursor, is active against p-toluene sulfonyl L-arginine methyl ester and N-acetyl L-tyrosine ethyl ester, is not inhibited by soybean trypsin inhibitor, and does not digest casein. In view of the evidence that chloroform, peptone and antigen-antibody activate a similar, if not identical, proesterase, which is distinct from plasminogen, the possible role of this enzymic activity in histamine release is considered.