Comparative Study of Action of Cell Wall Proteinases from Various Strains of Streptococcus cremoris on Bovine α s1 -, β-, and κ-Casein

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Abstract
Partially purified cell wall proteinases of eight strains of Streptococcus cremoris were compared in their action on bovine α s1 -, β-, and κ-casein, as visualized by starch gel electrophoresis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and thin-layer chromatography. Characteristic degradation profiles could be distinguished, from which the occurrence of two proteinases, represented by strain HP and strain AM 1 , was concluded. The action of the HP-type proteinase P 1 (also detectable in strains Wg 2 , C 13 , and TR) was established by electrophoretic methods to be directed preferentially towards β-casein. The AM 1 -type proteinase P III (also detectable in strain SK 11 ) was also able to degrade β-casein, but at the same time split α s1 - and κ-casein more extensively than did P I . Strain FD 27 exhibited mainly P I activity but also detectable P III degradation characteristics. The cell wall proteinase preparation of strain E 8 showed low P I as well as low P III activity. All proteinase preparations produced from κ-casein positively charged degradation products with electrophoretic mobilities similar to those of degradation products released by the action of the milk-clotting enzyme chymosin. The differences between P I and P III in mode of action, as detected by gel electrophoresis and thin-layer chromatography, were reflected by the courses of the initial degradation of methyl - 14 C-labeled β-casein and by the effect of α s1 - plus κ-casein on these degradations. The results are discussed in the light of previous comparative studies of cell wall proteinases in strains of S. cremoris and with respect to the growth of this organism in milk.