Developmental aspects of galactose-1-phosphate uridylytransferase in rat intestine.

Kinetic and developmental characteristics of rat jejunal galactose-1-phosphate uridylyltransferase have been examined. Km values for the substrates galactose-1-phosphate and uridine diphosphate (UDP) glucose were the same for both the newborn and adult rat enzymes, although the Vmax of the enzyme in newborns was about threefold higher than that of the adult rat. Equal enzyme activity was present in the villus, crypt cells and the muscularis of adult jejunum. The specific activity of the enzyme remained relatively uniform (V about 20 nmoles/min/mg protein) until 18 days of age when the velocity of the reaction began to decrease. The adult value at 42 days of age is about one fifth of that in the young. The pattern of change of specific activity was compared with that for galactokinase and UDP-galactose-4-epimerase, and the observations suggest separated regulatory factors for each enzyme. The total activity of the galactose-metabolizing enzymes in jejunum was also calculated. In the young, transferase has the highest activity, but in the adult, epimerase activity is highest. Jejunal galactokinase activity is low throughout the developmental period which suggests that phosphorylation of galactose may be the limiting step in intestinal metabolism of the sugar.