Open AccessProperties of Galactosyltransferase‐Enriched Vesicles of Golgi Membranes from Lactating‐Rat Mammary Gland
Author(s) -
KUHN Nicholas J.,
WOODING F. B. Peter,
WHITE Adrian
Publication year - 1980
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1980.tb04324.x
Subject(s) - vesicle , galactosyltransferase , golgi apparatus , lactose , chemistry , membrane , galactose , alpha lactalbumin , anomer , lactalbumin , biochemistry , chromatography , endoplasmic reticulum , enzyme
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 K m of 1.5 mM was shown towards glucose at anomeric equilibrium, but only β‐glucose was utilised. Two apparent K m values, about 17 μM and 112 μM, were shown towards UDP‐galactose. 5‐ d ‐Thioglucose, 6‐deoxy‐ d ‐glucose and 6‐deoxy‐6‐chloro‐ d ‐glucose were alternative substrates, acquiring α‐lactalbumin dependence when the vesicles were lysed with detergent. Substrates independent of α‐lactalbumin, or inhibited by it, included a wide range of, N ‐acylated glucosamines as well as phenyl‐β‐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.