Van Veldhoven P P, Mannaerts G P
Katholieke Universiteit Leuven, Afdeling Farmakologie, Belgium.
Adv Exp Med Biol. 1999;466:261-72. doi: 10.1007/0-306-46818-2_31.
In mammals, peroxisomes are involved in breakdown of very long chain fatty acids, prostanoids, pristanic acid, dicarboxylic fatty acids, certain xenobiotics and bile acid intermediates. Substrate spectrum and specificity studies of the four different beta-oxidation steps in rat and/or in man demonstrate that these substrates are degraded by separate beta-oxidation systems composed of different enzymes. In both species, the enzymes acting on straight chain fatty acids are palmitoyl-CoA oxidase, an L-specific multifunctional protein (MFP-1) and a dimeric thiolase. In liver, bile acid intermediates undergo one cycle of beta-oxidation catalyzed by trihydroxycoprostanoyl-CoA oxidase (in rat), or branched chain acyl-CoA oxidase (in man), a D-specific multifunctional protein (MFP-2) and SCPX-thiolase. Finally, pristanic acid is degraded in rat tissues by pristanoyl-CoA oxidase, the D-specific multifunctional protein-2 and SCPX-thiolase. Although in man a pristanoyl-CoA oxidase gene is present, so far its product has not been found. Hence, pristanoyl-CoA is believed to be desaturated in human tissues by the branched chain acyl-CoA oxidase. Due to the stereospecificity of the oxidases acting on 2-methyl-branched substrates, an additional enzyme, 2-methylacyl-CoA racemase, is required for the degradation of pristanic acid and the formation of bile acids.
在哺乳动物中，过氧化物酶体参与极长链脂肪酸、前列腺素、降植烷酸、二羧酸脂肪酸、某些外源性物质和胆汁酸中间体的分解代谢。对大鼠和/或人类中四个不同β-氧化步骤的底物谱和特异性研究表明，这些底物由不同酶组成的独立β-氧化系统降解。在这两个物种中，作用于直链脂肪酸的酶是棕榈酰辅酶A氧化酶、一种L特异性多功能蛋白（MFP-1）和一种二聚体硫解酶。在肝脏中，胆汁酸中间体经历一个由三羟基粪甾烷酰辅酶A氧化酶（在大鼠中）或支链酰基辅酶A氧化酶（在人类中）、一种D特异性多功能蛋白（MFP-2）和SCPX-硫解酶催化的β-氧化循环。最后，降植烷酸在大鼠组织中由降植烷酰辅酶A氧化酶、D特异性多功能蛋白-2和SCPX-硫解酶降解。虽然在人类中存在降植烷酰辅酶A氧化酶基因，但迄今为止尚未发现其产物。因此，降植烷酰辅酶A被认为在人体组织中由支链酰基辅酶A氧化酶去饱和。由于作用于2-甲基支链底物的氧化酶具有立体特异性，降植烷酸的降解和胆汁酸的形成需要一种额外的酶，即2-甲基酰基辅酶A消旋酶。
