Ascorbate is consumed stoichiometrically in the uncoupled reactions catalyzed by prolyl 4-hydroxylase and lysyl hydroxylase.
Ascorbate is consumed stoichiometrically in the uncoupled reactions catalyzed by prolyl 4-hydroxylase and lysyl hydroxylase.
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DOI：
10.1016/s0021-9258(18)91023-9
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发表时间：
1984-05
期刊：
影响因子：
--
通讯作者：
Raili Myllylä;Kari Majamaa;Volkmar Gunzler;H. Hanauske-Abel;Kari I. Kivirikko
中科院分区：
文献类型：
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作者：
Raili Myllylä;Kari Majamaa;Volkmar Gunzler;H. Hanauske-Abel;Kari I. Kivirikko
胶原羟化酶对脯氨酸和赖氨酸残基的羟基化与2-酮戊二酸的化学计量脱羧偶联。抗坏血酸实际上是这些酶的特定需求，但以前的研究表明，它在大多数催化循环中不被消耗。脯氨酰4-羟化酶和赖氨酰羟化酶也已知在不存在肽底物的情况下催化2-酮戊二酸的解偶联脱羧。它在这里示出，不像完全的羟基化反应，未偶联的脱羧反应涉及化学计量的抗坏血酸消耗。当通过加入聚（L-脯氨酸）增强解偶联脯氨酰4-羟化酶反应的速率时，也可以看到这种化学计量的抗坏血酸消耗。由于胶原羟化酶可以催化偶联反应循环，即使在肽底物的存在下，抗坏血酸在这些反应中的主要功能，在体内被认为是重新激活的酶后，这样的解偶联循环。
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.