Properties of galactosyltransferase-enriched vesicles of Golgi membranes from lactating-rat mammary gland.
Lactose was synthesised within the lumen of purified Golgi membrane vesicles, prepared from lactating rat mammary gland, from externally added glucose and UDP-galactose. An apparent Km of 1.5 mM was shown towards glucose at anomeric equilibrium, but only beta-glucose was utilised. Two apparent Km values, about 17 micro M and 112 micro M, were shown towards UDP-galactose. 5-D-Thioglucose, 6-deoxy-D-glucose and 6-deoxy-6-chloro-D-glucose were alternative substrates, acquiring alpha-lactalbumin dependence when the vesicles were lysed with detergent. Substrates independent of alpha-lactalbumin, or inhibited by it, included a wide range of N-acylated glucosamines as well as phenyl-beta-glucoside. The galactosylation of these by vesicle preparations could be ascribed to a proportion of leaky vesicles. Suitably low concentrations of Triton X-100 activated lactose synthesis by intact vesicles, indicating the membrane as a rate-limiting feature of the system.
D000818:Animals; D002458:Cell Fractionation; D005260:Female; D005700:Galactosyltransferases / Q000378:metabolism*; D006056:Golgi Apparatus / Q000201:enzymology* / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000201:enzymology / Q000648:ultrastructure; D007700:Kinetics; D007774:Lactation; D008297:Male; D008321:Mammary Glands, Animal / Q000201:enzymology*; D008854:Microscopy, Electron; D011247:Pregnancy; D051381:Rats; D013379:Substrate Specificity
D005700:Galactosyltransferases