Studies on Galactosyltransferase

Abstract Investigations have been made of the kinetic effects of α-lactalbumin on the reactions catalyzed by galactosyltransferase using both N-acetylglucosamine and glucose as galactosyl group acceptors. The results indicate that α-lactalbumin can cause (a) the reactions to occur via alternative pathways, (b) reductions in the apparent Michaelis constant values for both substrates, (c) a decrease in the apparent maximum velocity of the reaction with N-acetylglucosamine, and (d) an increase in the apparent maximum velocity of the reaction with glucose. Further, it has been shown that α-lactalbumin enhances the substrate inhibition by N-acetylglucosamine and glucose, as well as the dead-end inhibition by l-arabinose and N-acetylgalactosamine. The general conclusion has been reached that α-lactalbumin is a special type of modifier which combines with the enzyme only after the addition of a carbohydrate reactant.