Characteristics of an Endocellular Proteolytic Enzyme System of Streptococcus Lactis

Cell-free extracts prepared from S. lactis grown in either milk or vitamin-test casein medium, showed the presence of a heat-labile proteolytic enzyme system with optimum activity against milk, casein, and lactalbumin at pH values near neutrality. Some of the characteristics of this enzyme system have been studied. The presence in the broth growth medium of casein and nicotinic acid increased the proteolytic activity of the cell-free extract. The low level of proteolytic activity at pH 5.0 would seem to limit the activity in cheese of most common types and in other acid dairy products.