Abstract
Uridine diphosphate- d -glucose-glycogen glucosyltransferase (UDPglucose: α-1,4-glucan α-4-glucosyltransferase, EC 2.4.1.11), the enzyme which catalyzes the synthesis of α-1,4-glucosyl residues of glycogen from UDP- d -glucose, was purified approx. 20-fold from lactating mammary gland extracts by ammonium sulfate fractionation, protamine precipitation and chromatography on TEAE-cellulose. The purified enzyme required d -glucose -6-P for maximal activity and the extent of activation, 2 to 3-fold, was found to be dependent on the concentration of UDP- d -glucose and glycogen. The pH optimum of the reaction, in the presence or absence of d -glucose -6-P , was approx. 6.5. The apparent Michaelis constant for UDP- d -glucose was 5·10 −4 M in the presence of d -glucose -6-P and 2·10 −3 M in the absence of this phosphate ester. The glucosyltransferase activity was found to be located almost exclusively in the soluble subcellular fraction in this tissue.
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