赖氨酸分解代谢
中文名称
通路描述
在人类中，大多数赖氨酸的分解代谢通常通过七步反应进行，这些反应最终汇入脂肪酸分解代谢途径。在前两步中，由单一酶复合物催化的赖氨酸与α-酮戊二酸结合形成苏拉糖醇，随后被裂解并氧化，产生谷氨酸和α-酮戊二酸半醛。后者分子进一步氧化为α-酮戊二酸。α-酮戊二酸被α-酮戊二酸脱氢酶复合物（负责在三羧酸循环中将α-酮戊二酸转化为琥珀酰-CoA 的同一酶复合物）氧化脱羧，生成谷酰-CoA。谷酰-CoA 转化为顺-2-丁烯酰-CoA，顺-2-丁烯酰-CoA 转化为β-羟基丁酰-CoA，β-羟基丁酰-CoA 转化为乙酰乙酰-CoA。因此，赖氨酸分解代谢的产物是 exclusively ketogenic 的；即在饥饿条件下，它们可用于酮体（β-羟基丁酸和乙酰乙酸）的合成，但不能用于净合成葡萄糖（Cox 2001; Goodman and Freeman 2001）。
英文描述
Lysine catabolism In humans, most catabolism of L-lysine normally proceeds via a sequence of seven reactions which feeds into the pathway for fatty acid catabolism. In the first two reactions, catalyzed by a single enzyme complex, lysine is combined with alpha-ketoglutarate to form saccharopine, which in turn is cleaved and oxidized to yield glutamate and alpha-ketoadipic semialdehyde. The latter molecule is further oxidized to alpha-ketoadipate. Alpha-ketoadipate is oxidatively decarboxylated by the alpha-ketoglutarate dehydrogenase complex (the same enzyme complex responsible for the conversion of alpha-ketoglutarate to succinyl-CoA in the citric acid cycle), yielding glutaryl-CoA. Glutaryl-CoA is converted to crotonyl-CoA, crotonyl-CoA is converted to beta-hydroxybutyryl-CoA, and beta-hydroxybutyryl-CoA is converted to acetoacetyl-CoA. The products of lysine catabolism are thus exclusively ketogenic; i.e., under starvation conditions they can be used for the synthesis of ketone bodies, beta-hydroxybutyrate and acetoacetate, but not for the net synthesis of glucose (Cox 2001; Goodman and Freeman 2001).
所含基因
9 个基因