Human urinary prokallikrein: rapid purification and model activation by trypsin.

With only a three-step chromatographic procedure, human urinary prokallikrein has been purified completely. The active kallikrein also could be purified in the process of this purification. The prokallikrein was very rapidly activated by trypsin, followed thereafter by a very slow increase in the kallikrein activity. In the rapidly activated state, the molecular weight and the values of Km and Vmax were very similar to those of the purified active kallikrein. Only the slow increase in the activity was observed by tryptic digestion of the active kallikrein. The results suggest that the initial rapid activation is due to release of the propeptide and the slow reaction is due to a limited hydrolysis of the activated prokallikrein at sites which are not directly related to the active site.