Acid Phosphatase in Cream and in Skimmilk

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Abstract
Acid phosphatase activity in cream is about twice that in skim milk. The phosphatase in both is relatively heat stable; 70% of the activity remained after heating at 65[degree] C for 15 min. The enzymes from raw cream and raw skim milk 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 skim milk 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. KM values, pH activity curves, and the effect of inhibitors are reported from the purified acid phosphatase of cream and milk. These studies showed no significant difference between the 2 enzyme preparations.