Summary
Numerous chemical enzyme inhibitors were employed to determine the active polar groups
in the prothrombin, thrombin and autoprothrombin C molecules. Prothrombin and autoprothrombin
C activities were decreased by the reduction of disulfide bonds, but thrombin activity
was affected only at higher concentrations of reducing agent. Amino groups were not
essential for the activity of autoprothrombin C; however, the blocking of such groups
decreased the activities of prothrombin and thrombin. The blocking of carbonyl groups
decreased the activity of both prothrombin and autoprothrombin C, but thrombin was
not inactivated by hydroxylamine. The activities of none of the three were decreased
by sulfhydry] blocking agents. Nonspecific oxidizing agents reduced the activities
of all three molecules ; however, oxidizing agents which specifically oxidize sulfhydryl
groups, were incapable of decreasing the activities of prothrombin, thrombin or autoprothrombin
C. The sulfhydryl groups are not essential for the activities of prothrombin, thrombin
or autoprothrombin C.