Myllylä R, Majamaa K, Günzler V, Hanauske-Abel H M, Kivirikko K I
J Biol Chem. 1984 May 10;259(9):5403-5.
The hydroxylation of proline and lysine residues by the collagen hydroxylases is coupled with a stoichiometric decarboxylation of 2-oxoglutarate. Ascorbate is virtually a specific requirement for these enzymes, but previous studies have demonstrated that it is not consumed during most catalytic cycles. Prolyl 4-hydroxylase and lysyl hydroxylase are known also to catalyze an uncoupled decarboxylation of 2-oxoglutarate in the absence of the peptide substrate. It is shown here that, unlike the complete hydroxylation reaction, the uncoupled decarboxylation reaction involves stoichiometric ascorbate consumption. This stoichiometric ascorbate consumption was also seen when the rate of the uncoupled prolyl 4-hydroxylase reaction was enhanced by the addition of poly(L-proline). Since collagen hydroxylases may catalyze occasional uncoupled reaction cycles even in the presence of the peptide substrates, the main function of ascorbate in these reactions in vivo is suggested to be that of reactivating the enzymes after such uncoupled cycles.
胶原蛋白羟化酶对脯氨酸和赖氨酸残基的羟基化作用与2-氧代戊二酸的化学计量脱羧反应相偶联。抗坏血酸实际上是这些酶的特异性需求物质，但先前的研究表明，在大多数催化循环中它不会被消耗。已知脯氨酰4-羟化酶和赖氨酰羟化酶在没有肽底物的情况下也能催化2-氧代戊二酸的非偶联脱羧反应。本文表明，与完整的羟基化反应不同，非偶联脱羧反应涉及化学计量的抗坏血酸消耗。当通过添加聚（L-脯氨酸）提高非偶联脯氨酰4-羟化酶反应的速率时，也观察到了这种化学计量的抗坏血酸消耗。由于即使在存在肽底物的情况下，胶原蛋白羟化酶也可能偶尔催化非偶联反应循环，因此抗坏血酸在体内这些反应中的主要功能被认为是在这种非偶联循环后使酶重新活化。
