The tertiary phase of rennin action on αs- and β-caseins

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Abstract
Summary: Casein, whole αs-casein and β-casein were incubated for 3 and 14 h with crystalline rennin, at pH 6·60 and 36 °C, both in phosphate buffer and in milk dialysate. Products obtained from both systems, comprising 30–83% calciumsensitive (Cas) components, gave similar patterns on starch gel electrophoresis. Whole casein and whole αs-casein were not so soluble in milk dialysate as in phosphate buffer. No significant differences in composition were observed between the Casand the calcium-insensitive (Ca1) products from the same source.The αs1-component of the Casproduct from rennin-treated whole αs-casein had faster gel mobility in comparison to the αs1-component in the Casproduct from untreated whole αs-casein. Also, αs1-casein yielded one faster-moving degradation product, while αs2,3,4appeared unaltered after 14h. The Casproduct of rennintreated β-casein also had faster mobility than untreated β-casein and yielded one faster degradation product and several minor ones of slower mobility. Arginine was the onlyN-terminal amino acid found in the Casproduct of both rennin-treated and untreated αs- and β-caseins. The arginine content increased from 3·48 and 4·98 moles/105g to 5·12 and 6·38 moles/105g in the Casproducts from rennin-treated β-and αs-caseins, respectively.