DESATURATION OF POLYUNSATURATED FATTY-ACIDS IN MUCOR-CIRCINELLOIDES AND THE INVOLVEMENT OF A NOVEL MEMBRANE-BOUND MALIC ENZYME
DESATURATION OF POLYUNSATURATED FATTY-ACIDS IN MUCOR-CIRCINELLOIDES AND THE INVOLVEMENT OF A NOVEL MEMBRANE-BOUND MALIC ENZYME
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DOI：
10.1111/j.1432-1033.1992.tb17334.x
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发表时间：
1992-10-15
期刊：
影响因子：
--
通讯作者：
RATLEDGE, C
中科院分区：
文献类型：
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作者：
KENDRICK, A;RATLEDGE, C
1.毛霉微粒体制剂的内源磷脂的脂肪酸成分，在30℃下振荡时，链长和不饱和度均增加。净效应是产生了 γ-亚麻酸，在 2 小时内，其占总脂肪酸的比例从 17% 增加到 32%。此后没有发生进一步的重大变化。2．去饱和/延伸反应的主要位点位于 Ptdlns 的 sn-2 位置。 PtdCho和PtdEtn没有受到牵连。3．在添加到微粒体的众多代谢物和辅因子中，只有苹果酸可以将延伸/去饱和反应延长长达 6 小时。这种效应被证明是由于膜相关的苹果酸酶 [苹果酸脱氢酶（脱羧）NADP+] 产生的 NADPH 用于脂肪酸去饱和。4。胞质酶和微粒体酶的动力学分析[均为 0.1%（质量/体积）Chaps]无法区分它们。然而，当微粒体苹果酸酶被透析去除Chaps时，它失去了90%的活性，而胞质苹果酸酶仅失去了20%的活性。5．苹果酸的结构类似物丙醇二酸是苹果酸酶的抑制剂，也能抑制苹果酸诱导的微粒体膜脂肪酰基去饱和和伸长的刺激。6．结论是存在两种不同的苹果酸酶，一种是可溶性的，一种是膜结合的，具有相似的活性位点。两者在 NADPH 的产生（用于脂质代谢）中具有不同的作用。前者产生用于脂肪酸生物合成的NADPH，而后者产生用于脂肪酸去饱和的NADPH。
1. The component fatty acids of the endogenous phospholipids of microsomal preparations of Mucor, when shaken at 30-degrees-C, increased in both chain length and in degree of unsaturation. The net effect was the production of gamma-linolenic acid which, over 2 h, increased from 17% to 32% of total fatty acids present. No further significant changes occurred after this time.2. The major site for desaturation/elongation reactions was at the sn-2 position of Ptdlns. PtdCho and PtdEtn were not implicated.3. Of numerous metabolites and cofactors-added to the microsomes, only malate could prolong the elongation/desaturation reactions for up to 6 h. This effect was shown to be due to a membrane-associated malic enzyme [malate dehydrogenase (decarboxylating) NADP+] with the NADPH produced being used in fatty-acid desaturation.4. Kinetic analysis of cytosolic and microsomal enzymes [both in 0.1% (mass/vol.) Chaps] could not distinguish between them. However, when the microsomal malic enzyme was dialysed to remove Chaps, it lost 90% of activity, although the cytosolic malic enzyme lost only 20% activity.5. The structural analogue of malate, tartronic acid, which is an inhibitor of malic enzyme, also inhibited the malate-induced stimulation of fatty-acyl group desaturation and elongation in the microsomal membranes.6. It is concluded that two distinct malic enzymes exist, one soluble and one membrane bound, with similar active sites. Both have different roles in the production of NADPH, for lipid metabolism. The former will produce NADPH for fatty-acid biosynthesis whilst the latter produces NADPH for fatty-acid desaturation.