BIOSYNTHESIS OF MARSUPIAL MILK OLIGOSACCHARIDES - CHARACTERIZATION AND DEVELOPMENTAL-CHANGES OF 2 GALACTOSYLTRANSFERASES IN LACTATING MAMMARY-GLANDS OF THE TAMMAR WALLABY, MACROPUS-EUGENII

Tammar wallaby (Macropus eugenii) mammary glands contain two galactosyltransferases of which the first, 4-beta-GalT, is a UDP-galactose: N-acetylglucosaminyl beta-1 --> 4-galactosyltransferase equivalent to the A protein of the lactose synthase of eutherian mammals. The second enzyme, 3-beta-GalT, is a UDP-galactose: lactose beta-1 --> 3-galactosyltransferase, not previously identified in mammary glands of any species, which catalyses the formation of Gal-beta-1 --> 3Gal-beta-1 --> 4Glc from lactose. The two enzyme activities, as well as the lactose synthase activity, have been characterised with respect to the effects of pH, apparent K(m) values, effects of bovine and tammar alpha-lactalbumins, heat sensitivity and identity of products. Studies on the substrate specificity and heat sensitivity of the 3-beta-GalT activity suggest that this enzyme may catalyse the beta-galactosylation of Gal-beta-1 --> 3Gal-beta-1 --> 4Glc as well as of lactose. The activity of the 3-beta-GalT, unlike that of the 4-beta-GalT, changes dramatically during the course of lactation in parallel with similar changes in the carbohydrate content of tammar milk.