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J. WENDELL DAVIS, DERRILL J. HEILAND, CHARLES D. SHORT, Pyrophosphate Phosphohydrolase in Mammary Tissue of Pregnant and Lactating Rats, Endocrinology, Volume 81, Issue 4, 1 October 1967, Pages 899–903, https://doi.org/10.1210/endo-81-4-899
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The activities of pyrophosphate phosphohydrolase in the soluble fraction of mammary tissue of rats at various stages of pregnancy or lactation were assessed under conditions which provided optimum rates of hydrolysis of the substrate. Accurate assessment of the activity of this enzyme in mammary tissue depends upon adequate removal of calcium ion from preparations of the gland. Subsequent incubation of the enzyme with 2-mercaptoethanol for 10 min prior to addition of pyrophosphate provided activities above those obtained by removal of calcium alone. During the last third of pregnancy, the specific activity of the enzyme rose rapidly but leveled off as the end of pregnancy was approached.approached. Beyond parturition, only a small, insignificant increase in specific activity could be measured. The activity of this enzyme increases in a manner similar to the increase in DNA content of the tissue in accord with the concept that this enzyme may be constitutive to the presecretory, epithelial cells of the gland. Failure of the enzymatic activity to increase markedly at parturition or upon ovariectomy of pregnant rats clearly demonstrates that the activity of pyrophosphate phosphohydrolase is not promoted by biosynthesis of new RNA which occurs with onset of lactation. (Endocrinology81: 899, 1967)