Effect of casein and casein phosphopeptides addition on chymosin production. A. Serial dilutions (1/2) of a pure preparation of chymosin (500 ng in 175 μl). B. Culture supernatants from strains TAPL-4, T7-36 and TG-87 cultured in the absence (-) or presence of either casein or phosphopeptides (CPP) were serially diluted from 1/2 to 1/512 (DF). No dilution is denoted as WD. The number of wells where milk clotting takes place (white precipitate) is proportional to the concentration of chymosin that is present in the culture supernatant. The chymosin concentration range that is present in those wells with positive clotting, has been determined using the data obtained from panel A as indicated in the Methods section.