生物素代谢
中文名称
通路描述
生物素（维生素 H 或维生素 B7）是生物素依赖性羧基酶的必需辅因子，如丙酮酸羧激酶和乙酰辅酶 A 羧激酶。哺乳动物无法合成生物素，而细菌、真菌和植物则通过不同途径从丙氨酸硫酯合成生物素。在 E. coli 和许多生物中，丙氨酸硫酯来源于丙二酰辅酶 A。该途径始于丙二酰辅酶 A 甲基酯的形成，随后进行脂肪酸链延长循环形成丙酰辅酶 A 甲基酯，然后脱甲基形成丙酰辅酶 A。丙酰辅酶 A 通过生物素双环组装的最后四个步骤转化为生物素，这些步骤在生物素产生生物体中保守存在。在枯草芽孢杆菌中，生物素来源于丙酰辅酶 A，该辅酶 A 由长链酰辅酶 A 的氧化裂解形成。某些细菌从丙氨酸衍生出的丙酰辅酶 A 合成生物素。生物素由生物素蛋白连接酶共价连接到生物素依赖性羧基酶上，也称为哺乳动物中的全羧基酶合成酶，形成活性全羧基酶。生物素化羧基酶降解后形成生物素，进一步被生物素酶降解以释放游离生物素，该游离生物素在羧基酶合成中循环。生物素通过戊酸侧链的β-氧化或环状杂环中硫的氧化进行降解。
英文描述
Biotin (vitamin H or vitamin B7) is the essential cofactor of biotin-dependent carboxylases, such as pyruvate carboxylase and acetyl-CoA carboxylase. Mammals cannot synthesize biotin, while in bacteria, fungi, and plants it is synthesized from pimelate thioester through different pathways. In E. coli and many organisms, pimelate thioester is derived from malonyl-ACP. The pathway starts with the methylation to malonyl-ACP methyl ester, followed by the fatty acid chain elongation cycle to form pimeloyl-ACP methyl ester, which is then demethylated to form pimeloyl-ACP [MD:M00572]. Pimeloyl-ACP is converted to biotin through the final four steps in the biotin bicyclic ring assembly, which are conserved among biotin-producing organisms [MD:M00123]. In B. subtilis, biotin is derived from pimeloyl-ACP formed by oxidative cleavage of long-chain acyl-ACPs [MD:M00573]. Some bacteria synthesize biotin from pimeloyl-CoA derived from pimelate [MD:M00577]. Biotin is covalently attached to biotin-dependent carboxylase by biotin protein ligase, also known as holocarboxylase synthase in mammals, to form an active holocarboxylase. After degradation of the biotinylated carboxylase into biocytin, it is further degraded by biotinidase to release free biotin, which is recycled in holocarboxylase synthesis. Biotin is catabolized by beta-oxidation of the valeric acid side chain or oxidation of sulfur in the heterocyclic ring.
所含基因
3 个基因