Physiological roles of zinc and calcium binding to alpha-lactalbumin in lactose biosynthesis.
Physiological roles of zinc and calcium binding to alpha-lactalbumin in lactose biosynthesis.
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锌和钙与α-乳白蛋白结合在乳糖生物合成中的生理作用。
DOI：
10.1021/bi00345a029
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发表时间：
1985
期刊：
影响因子：
2.9
通讯作者：
Berliner,LJ
中科院分区：
文献类型：
--
作者：
Musci,G;Berliner,LJ
牛脱辅基-α-乳白蛋白作为乳糖生物合成中的辅因子显示出比其钙构象体高几倍的效率。这种速率增强表现为Kmax增加3.5倍，两种乳清蛋白形式之间的Km（app）无差异。在锌的存在下，其使Ca（II）-α-乳白蛋白向“apo样”构象移动[Musci，G.，& Berliner，L. J.（1985）Biochemistry 24，3852-3856]，乳糖合成的催化速率常数对于Ca（II）和apo构象异构体是相同的。在不同温度下的活性测量，另一方面，证实钙是重要的稳定蛋白质（-乳白蛋白）对热变性。钙的稳定作用是独立的Zn（II）的存在下，即蛋白质构象。修饰蛋白α-乳白蛋白（-LA）1是乳糖合成酶复合物（UDP-半乳糖：o-葡萄糖4-β 3-D-半乳糖基转移酶，EC 2.4）的非催化调节亚基。1.22）。LA与半乳糖基转移酶（GT）的关联赋予后者的酶从末端A-乙酰葡糖胺受体到葡萄糖的特异性的变化。先前
Bovine apo-a-lactalbumin was shown to be severalfold more efficient than its calcium conformer as a cofactor in lactose biosynthesis. This rate enhancement was manifested in a 3.5-fold increase in Kmax, with no differences in Km (app) between the two-lactalbumin forms. In the presence of zinc, which shifts Ca (II)-a-lactalbumin toward the “apo-like” conformation [Musci, G., & Berliner, L. J.(1985) Biochemistry 24, 3852-3856], the catalytic rate constant for lactose synthesis was identical for both the Ca (II) and apo conformers. Activity measurements at different temperatures, on the other hand, confirmed that calcium is important in stabilizing the protein (-lactalbumin) against thermal denaturation. The stabilizing effect of calcium was independent of the presence of Zn (II), ie, of the protein conformation. The physiological implications of these results are discussed.The modifier protein a-lactalbumin (-LA) 1 is the nonca-talytic regulatory subunit of the “lactose” synthase complex (UDP-galactose: o-glucose 4-j3-D-galactosyltransferase, EC 2.4. 1.22). The association of-LA with galactosyltransferase (GT) imparts a change in specificity of the latter enzyme from terminal A-acetylglucosaminyl acceptors to glucose. Previous