Presence and Physiological Roles of Novel Biosynthetic Pathways of Long Chain Fatty Acyl-CoA.Long Chain Fatty Acyl-CoA.

长链脂肪酸酰基辅酶a是脂肪酸的一种代谢活性形式，哺乳动物组织中脂肪酸的各种酶促转化模式，包括去饱和、链延伸和氧化，主要以脂肪酸酰基辅酶a的形式发生。酰基辅酶a的另一个重要作用是作为酰基供体形成各种类型的简单辅助复合脂质分子。除了作为代谢中间体的作用外，酰基辅酶a还可以调节各种酶和细胞功能。对于酰基辅酶a的生物合成，已知长链酰基辅酶a合成酶催化游离脂肪酸与辅酶a的连接反应，消耗ATP。合成酶具有一个保守的atp结合位点，并包含一个基因家族。先前我们发现了另一种酰基辅酶a合成途径，涉及哺乳动物组织微粒体部分中atp非依赖性和辅酶a依赖性的酰基辅酶a合成。在没有ATP-Mg^<2+>的条件下，微粒体与CoA孵育可产生大量酰基CoA。我们认为新的酰基辅酶a合成活性可能是由于酰基辅酶a与溶血磷脂酰基转移酶的逆反应，因为发生了裂解磷脂酰胆碱（LPC）和溶血磷脂酰肌醇（LPI）等溶血磷脂的生成。为了澄清这一假设，我们研究了重组溶血磷脂酸（LPA）酰基转移酶（LPAAf）是否催化了atp非依赖性酰基辅酶a的形成。目前LPAAT基因转染细胞的结果揭示了磷脂酸（PA）形成atp非依赖性酰基辅酶a的机制。多项证据表明，这条酰基辅酶a合成途径是由LPAAT的逆反应引起的：这是除酰基辅酶a合成酶之外的第一个酰基辅酶a合成酶存在的直接和确凿证据，同时也揭示了LPAAT的新功能。该假设是否适用于其他酰基辅酶a：溶血磷脂酰基转移酶的问题需要考虑。我们试图纯化一种酰基辅酶a：溶血磷脂酰基转移酶LPI酰基转移酶（LPIAT），以检验LPIAT是否可以反向作用形成酰基辅酶a和LPI。在纯化过程中，LPIAT从其他酰基辅酶a酰基转移酶中分离出来。纯化的LPIAT片段显示ATP。-不依赖酰基辅酶a的合成活性和由PI产生的辅酶a依赖型LPI，表明LPIAT可以反向作用形成酰基辅酶a和LPI。综上所述，我们发现了一种基于LPAAT和LPIAT逆反应的不依赖atp的酰基辅酶a生物合成途径，这可能是其他微粒体磷脂合成其他不依赖atp的酰基辅酶a活性的原型。少

Long chain fatty acyl-CoA is a metabolically active form of fatty acid, and various modes of enzymatic, conversion of fatty acids, including desaturation, chain elongation and oxidation, occur mainly in the form of fatty acyl-CoA in mammalian tissues. Another important role, of acyl-CoA is as an acyl donor in the formation of various types of simple aiid complex lipid molecules. In addition to its role as a metabolic intermediate, acyl-CoA is known to modulate various enzyme and cell functions. As for the biosynthesis of acyl-CoA, long chain acyl-CoA synthetases are known to catalyze the ligation reaction of free fatty acid and CoA with the consumption of ATP. The synthetase enzymes possess a conserved ATP-binding site and comprise a gene family.Previously we found another acyl-CoA synthetic pathway, involving ATP-independent and coA-dependent synthesis of acyl-CoA in microsomal fractions of mammalian tissues. Substantial acyl-CoA was produced when microsomes were incubated with CoA in … More the absence of ATP-Mg^<2+>. We considered that the novel acyl-CoA synthetic activity may be due to the reverse reaction of acyl-CoA : lysophospholipid acyltransferases, because the generation of lysophospholipids, such as lysd phosphatidyicholine (LPC) and lysophosphatidylinositol (LPI), occurred. To clarify the hypothesis, we investigate d whether or not ATP-independent acyl-CoA formation catalyzed by recombinant lysophosphatidic acid (LPA) acyltransferase (LPAAf). The present results for LPAAT gene-transfected cells revealed a mechanism for ATP-independent acyl-CoA formation from phosphatidic acid (PA). Several lines of evidence indicate that this acyl-CoA synthetic route is due to the reverse reaction of LPAAT : This is the first direct and conclusive evidence for an acyl-CoA synthesizing enzyme other than acyl-CoA synthelase, and it also reveals a novel function for LPAAT.The question of whether or not the hypothesis is applies to other acyl-CoA : lysophospholipid acyltransferases needs to be considered. We tried to purify LPI acyltranferase (LPIAT), one of the acyl-CoA : lysophospholipid acyltransferases, in order to examine whether LPIAT could operate in reverse to form acyl-CoA and LPI. During the purification, LPIAT was separated from other acyl-CoA acyltransferases. The purified LPIAT fraction exhibited ATP.-independent acyl-CoA synthetic activity and CoA-dcpendent LPI generation from PI, suggesting that LPIAT could operate in reverse to form acyl-CoA and LPI.In conclusion, we have found an ATP-independent biosynthetic pathway for acyl-CoA, which is based on the reverse reaction of LPAAT and LPIAT which may be a prototype for other microsomal ATP-independent acyl-CoA synthetic activity from other phospholipids. Less