Studies on a proteolytic enzyme in human plasma; some factors influencing the enzymes activated by chloroform and by filtrates coccal fibrinolysin.

1. Some conditions for the optimal activation of plasma proteolytic enzyme by chloroform have been described. The activation proceeds slowly. The action of chloroform is probably to remove some substance which inhibits or inactivates the plasma proteolytic enzyme preparation, rather than a direct activation of the enzyme. 2. Plasma proteolytic enzyme is activated by filtrates of cultures of beta hemolytic streptococci. When streptococcal fibrinolysin is present in maximally effective amounts, the activation is almost instantaneous. When the globulin is prepared from heated serum or the globulin is treated with chloroform, the activation of enzyme by streptococcal fibrinolysin appears to be catalytic. If the globulin is not so treated, the reaction appears to involve a stoichiometric process. 3. The plasma proteolytic enzyme activated by chloroform or by streptococcal fibrinolysin digests casein in direct proportion to the concentration of enzyme and to the time of digestion, during the early period of incubation. 4. Fibrinolysin-activated enzyme deteriorates rapidly relative to chloroform-activated enzyme. This may be due to the removal by chloroform of some substance which inactivates plasma proteolytic enzyme.