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Developmental Aspects and Some Characteristics of Mammalian Galactose 1-Phosphate Uridyltransferase

From the ¹ From the Clinical Endocrinology Branch, National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland 20014

Galactose 1-phosphate uridyltransferase (EC 2.7.7.12: UDP-glucose:-d-galactose-1-phosphate uridylyltransferase) activity in the developing rat liver, gut, and kidney is presented. The activity in liver tissue increased from 3 days before birth to a maximum in the 10-day-old animal and then declined to adult levels between 35 and 45 days. No observed rise in transferase activity occurred in gut and kidney from term until 10 days with a subsequent decrease until 35 days. Adult rat brain and diaphragm were also examined for enzyme activity. By comparison at any age, liver had a consistently higher enzyme rate than any of the other tissues studied, and brain had the lowest in the adult tissues studied. The enzyme activity in liver of female adult rats was significantly lower than in the same aged male animals.

By differential centrifugation, transferase from newborn and adult rat liver was located entirely in the soluble fraction. The enzyme in newborn liver was 3 times more active and had V_max values 3 times greater than in the adult liver, but the enzyme from both preparations had the same (a) stability characteristics, (b) K_m values for galactose-1-P (1.39 x 10^-4 m) and for UDP-glucose (1.56 x 10^-4 m), (c) pH optimum (8.3 to 8.6), and (d) sulfhydryl requirements. In addition, both enzyme preparations utilized UDP-galactose as a substrate with galactose-1-P with the same K_m (1.67 x 10^-4 m), and neither was as sensitive to inhibition by this substrate as with galactose-1-P or UDP-glucose. The enzyme from both sources was more sensitive to UDP-glucose inhibition than galactose-1-P inhibition, but the enzyme from newborn liver was 3 times less sensitive to inhibition by either of these substrates than the enzyme from adult liver. Glucose-1-P caused marked inhibition of the enzyme from the adult liver.

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