The hydroxylation of CMP-N-acetylneuraminic acid (CMP-NeuAc) in the formation of CMP-N-glycolylneuraminic acid requires several components which comprise an electron transport system. A protein, which replaces one of the components, was purified to homogeneity from a horse erythrocyte lysate. Based on its partial amino acid sequence and immunological cross-reactivity, this protein was identified as soluble cytochrome b5 lacking the membrane domain of microsomal cytochrome b5. The electron transport system involved in CMP-NeuAc hydroxylation was reconstituted, and then characterized using the purified horse soluble cytochrome b5 and a fraction from mouse liver cytosol. The hydroxylation reaction requires a reducing reagent, DTT being the most effective. Either NADH or NADPH was used as an electron donor, but the activity with NADPH amounted to about 74% of that with NADH. The hydroxylation was inhibited by salts and azide due to interruption of the electron transport from NAD(P)H to cytochrome b5 and in the terminal enzyme reaction, respectively.

译文

:CMP-N-乙酰基神经氨酸的形成中的CMP-N-乙酰神经氨酸(CMP-NeuAc)的羟基化需要包含电子传输系统的几种组分。从马红细胞裂解物中纯化出一种蛋白质,以取代一种成分。根据其部分氨基酸序列和免疫交叉反应性,该蛋白被鉴定为缺乏微粒体细胞色素b5膜结构域的可溶性细胞色素b5。重建参与CMP-NeuAc羟基化的电子传输系统,然后使用纯化的马可溶细胞色素b5和来自小鼠肝细胞溶质的部分进行表征。羟基化反应需要还原剂,DTT是最有效的。 NADH或NADPH均用作电子供体,但NADPH的活性约为NADH的74%。分别由于电子从NAD(P)H到细胞色素b5的转移以及在末端酶反应中的中断,盐和叠氮化物抑制了羟基化作用。

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