胆固醇生物合成中C-4去甲基化的机制与调控研究。3':5'-环磷酸腺苷的作用。

Studies on the mechanism and regulation of C-4 demethylation in cholesterol biosynthesis. The role of adenosine 3':5'-cyclic monophosphate.

Bloxham D P, Wilton D C, Akhtar M

Biochem J. 1971 Nov;125(2):625-34. doi: 10.1042/bj1250625.

Abstract

An assay for demethylation has been developed based on the release of tritium from 4,4-dimethyl[3alpha-(3)H]cholest-7-en-3beta-ol (II). 2. The maximum release of (3)H from 3alpha-(3)H-labelled compound (II) in a rat liver microsomal preparation occurs in the presence of NADPH and NAD(+) under aerobic conditions. 3. Incubation of 3alpha-(3)H-labelled compound (II) with NADPH under aerobic conditions leads to the formation of a 3alpha-(3)H-labelled C-4 carboxylic acid. This compound undergoes dehydrogenation on subsequent anaerobic incubation with NAD(+). 4. The (3)H released from the steroid was located in [4-(3)H]nicotinamide and the medium. Incubation with synthetic [4-(3)H(2)]NADH gave a similar result. 5. In the presence of glutamate dehydrogenase and alpha-oxoglutarate part of the (3)H released from the steroid was transferred to glutamate. 6. A series of 3-oxo steroids were reduced equally well by [4-(3)H(2)]NADH and [4-(3)H(2)]NADPH. The reduction of 5alpha-cholest-7-en-3-one was shown to use the 4B H atom from the nucleotide. 7. 3':5'-Cyclic AMP was shown to be a competitive inhibitor of the 3beta-hydroxy dehydrogenase enzyme in the demethylation reaction.

摘要

基于从4,4-二甲基[3α-(³H)]胆甾-7-烯-3β-醇（II）中释放出氚，已开发出一种去甲基化测定法。
在有氧条件下，大鼠肝微粒体制剂中3α-(³H)标记化合物（II）的³H最大释放发生在存在NADPH和NAD⁺的情况下。
在有氧条件下，3α-(³H)标记化合物（II）与NADPH孵育会导致形成3α-(³H)标记的C-4羧酸。该化合物在随后与NAD⁺进行厌氧孵育时会发生脱氢反应。
从类固醇释放出的³H存在于[4-(³H)]烟酰胺和培养基中。与合成的[4-(³H₂)]NADH孵育得到了类似的结果。
在谷氨酸脱氢酶和α-酮戊二酸存在的情况下，从类固醇释放出的部分³H转移到了谷氨酸中。
一系列3-氧代类固醇被[4-(³H₂)]NADH和[4-(³H₂)]NADPH还原的效果相同。已证明5α-胆甾-7-烯-3-酮的还原使用了来自核苷酸的4B氢原子。
已证明3':5'-环磷酸腺苷是去甲基化反应中3β-羟基脱氢酶的竞争性抑制剂。