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Apyrase Activity of the Mammary Gland^{1, 2, 3,}

Laboratory of Biochemistry, Department of Dairy Science, University of Illinois, Urbana

ABSTRACT

An enzymatic hydrolysis of ATP by preparations of lactating rat mammary gland has been observed. The action was a linear function of time and protein concentration. Added magnesium ions depressed apyrase activity of homogenates made with phosphate buffer. In contrast, the addition of magnesium to water homogenates produced a stimulation. Fluoride inhibited the apyrase action of either preparation.

About 45% of the apyrase was extracted with water. The enzymatic activity of this extract was stimulated with either calcium or magnesium ions. The remaining apyrase was associated with cellular debris of the mammary tissue. Variation in the stimulation with ions suggested the presence of multiple enzymes. The enzymes in both fractions removed at least two phosphates from ATP.

¹ Preliminary report: J. Dairy Sci., 36: 589. 1953.

² A portion of these data was taken from a thesis presented by E. M. Craine to the Graduate Faculty of the University of Illinois to fulfill partial requirements for the degree of Doctor of Philosophy.

³ Supported in part by a grant from the United States Atomic Energy Commission [Contract No. AT (11-1)-67, Project No. 10].