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Acid Phosphatase in Cream and in Skimmilk

Eastern Regional Research Laboratory,¹ Philadelphia 18, Pennsylvania

ABSTRACT

Acid phosphatase activity in cream is about twice that in skimmilk. The phosphatase in both is relatively heat-stable; 70% of the activity remained after heating at 65° C. for 15 min. The enzymes from raw cream and raw skimmilk were each purified threefold. The cream enzyme was concentrated in the insoluble residue obtained by centrifuging the buttermilk fraction of washed cream at 50,000 x G for 1 hr. When skimmilk was centrifuged under the same conditions, most of the enzyme activity remained in the supernatant solution, which was further purified by ammonium sulfate treatment to yield a soluble form of acid phosphatase. Ultracentrifuge fractionation of buttermilk failed to concentrate the cream enzyme activity in a single fraction. Acid phosphatase, alkaline phosphatase, and xanthine oxidase activities were broadly distributed in these fractions. pH activity curves, K_M values, and the effect of inhibitors are reported for the purified acid phosphatase of cream and milk. These studies showed no significant difference between the two enzyme preparations.

¹ Eastern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.