Kuhn N J, Wooding F B, White A
Eur J Biochem. 1980 Jan;103(2):377-85. doi: 10.1111/j.1432-1033.1980.tb04324.x.
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.
乳糖是在从泌乳大鼠乳腺制备的纯化高尔基体膜囊泡的腔内，由外部添加的葡萄糖和UDP-半乳糖合成的。在异头物平衡时，对葡萄糖的表观Km值为1.5 mM，但仅利用β-葡萄糖。对UDP-半乳糖显示出两个表观Km值，约为17 μM和112 μM。5-D-硫代葡萄糖、6-脱氧-D-葡萄糖和6-脱氧-6-氯-D-葡萄糖是替代底物，当用去污剂裂解囊泡时获得α-乳白蛋白依赖性。独立于α-乳白蛋白或被其抑制的底物包括多种N-酰化葡糖胺以及苯基-β-葡萄糖苷。囊泡制剂对这些物质的半乳糖基化可归因于一定比例的渗漏囊泡。适当低浓度的 Triton X-100可激活完整囊泡的乳糖合成，表明膜是该系统的限速特征。
