Serine proteinases and their inhibitors in Phycomyces blakesleeanus

Three serine proteinases of Phycomyces blakesleeanus were isolated and characterized. The molecular weights were determined to be 18,000, 22,000, and 60,000. The proteinases were solubilized by detergent or salt treatment. Two soluble proteins that specifically inhibit these proteinases were also isolated and characterized. Both these proteins formed 1:1 complexes with the serine proteinases. A molecular weight of 10,000 was estimated for both inhibitors. They were found to be present in excess in the cells. An acid proteinase of Phycomyces was able to take the inhibitor off a serine proteinase.inhibitor complex. This proteinase was partially purified. The proteinases and inhibitors of three mutant strains were partially purified and compared with a standard strain. These mutants exhibit abnormal growth responses of the sporangiophore to light. Mutant specific changes of the proteinases and their inhibitors were detected, but a connection to the behavioral responses could not be demonstrated.