Inactivation of human plasma alpha 1-antichymotrypsin by microbial proteinases

Incubation of human plasma alpha 1-antichymotrypsin with proteinases from various microbial sources resulted in the enzymatic inactivation of the inhibitor as determined by loss of inhibitory activity against alpha-chymotrypsin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the reaction products indicated that intact alpha 1-antichymotrypsin (Mr 67000) had been converted to an inactive form (63000) by limited proteolysis. No stable proteinase/inhibitor complexes were detected, and no random proteolysis of the inactivated inhibitor occurred even after prolonged incubation with the proteinases. Metallo- and serine proteinases from several microbial sources all readily inactivated alpha 1-antichymotrypsin. Since alpha 1-antichymotrypsin is also an early stage acute phase reactant, its inactivation may be important in disrupting bodily defense mechanisms.