Partial Isolation and Degradation of Caseins by Cell Wall Proteinase(s) of Streptococcus cremoris HP

Abstract

The cell wall proteinase fraction of Streptococcus cremoris HP has been isolated. This preparation did not exhibit any activity due to either specific peptidases known to be located near the outside surface of and in the membrane or intracellular proteolytic enzymes. By using thin-layer chromatography for the detection of relatively small hydrolysis products which remain soluble at pH 4.6, it was shown that beta-casein is preferentially attacked by the cell wall proteinase. This was also the case when whole casein or micelles were used as the substrate. kappa-casein hydrolysis is a relatively slow process, and alpha(s)-casein degradation appeared to proceed at an extremely low rate. These results could be confirmed by using CH(3)-labeled caseins. A relatively fast and linear initial progress of CH(3)-labeled beta-casein degradation is not inhibited by alpha(s)-casein and only slightly by kappa-casein at concentrations of these components which reflect their stoichiometry in the micelles. Possible implications of beta-casein degradation for growth of the organism in milk are discussed.