2-Oxoglutarate-linked, iron-containing

Ascorbic acid has specific and weU-deflned roles in two classes of enzymes the copper-containing hydroxylases (such as dopamine /3-hydroxylase and peptidyl glycine hydroxylase) and the 2-oxoglutarate-linked iron-containing hydroxylases, of which the best studied are the proline and lysine hydroxylases involved in maturation of connective tissue (and other) proteins. 

As shown in Table 13.1, a number of iron-containing hydroxylases share an unusual reaction mechanism in which hydroxylation of the substrate is linked to decarboxylation of 2-oxoglutarate. Proline and lysine hydroxylases are required for the postsynthetic modification of collagen, and proline hydroxylase also for the postsynthetic modification of osteocalcin (Section 5.3.3) and other proteins. Aspartate /3-hydroxylase is required for the postsynthetic modification of protein C, the vitamin K-dependent protease that hydrolyzes activated Factor V in the blood clotting cascade (Section 5.3.2). Trimethyllysine and y-butyrobetaine hydroxylases are required for the synthesis of carnitine (Section 14.1.1). 

A number of iron-containing hydroxylases (Table 1) share a common reaction mechanism, in which hydroxylation of the substrate is linked to decarboxylation of 2-oxoglutarate. Ascorbate is required for... 

---