Proteinase activity of dairy Propionibacterium

A proteolytic system was found in all the species of dairy Propionibacterium. Two types of activities could act on ¹⁴C] \gb-casein or ¹⁴C] \ga_s1-casein. The first was the highest at the beginning of the exponential growth phase, tightly linked to the cells and hydrolysed preferably \gb-casein. The second was released at the end of growth and acted similarly on both substrates tested. This activity was located in the cell membrane of these cheese-ripening bacteria. The enzyme could be gently extracted from the cell by incubation in Ca^2\s+ \t- or Mg Mg^2\s+-free buffer.