Characterization of an Intracellular Proteinase of a Slow Acid Producing Mutant of Streptococcus lactis

An intracellular proteinase was purified 152-fold from a slow acid producing mutant of Streptococcus lactis No. 3 with gel and ion exchange chromatography. Homogeneity was established by polyacrylamide gel and cellulose-acetate strip electrophoresis, sedimentation velocity, and sedimentation equilibrium analysis. Several properties of the enzyme were determined and compared to those previously reported for the parent intracellular proteinase. The intracellular proteinase of the mutant differed from the parent intracellular proteinase in every property examined. The mutant enzyme was most active on casein at ptt 7.6, was unaffected by p-hydroxymercuribenzoate or iodoacetate, was labile to storage at 3 C, had a molecular weight of 13,335 and a sedimentation coefficient of 1.91S.