Ascorbate is consumed stoichiometrically in the uncoupled reactions catalyzed by prolyl 4-hydroxylase and lysyl hydroxylase

• Published in: The Journal of biological chemistry 1984-05, Vol.259 (9), p.5403-5405
• Main Authors: Myllylä, R, Majamaa, K, Günzler, V, Hanauske-Abel, H M, Kivirikko, K I
• Format: Article
• Language: English
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Ascorbic Acid - metabolism; Biological and medical sciences; Carbon Radioisotopes; Chick Embryo; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Glutarates - metabolism; Kinetics; Mixed Function Oxygenases - metabolism; Oxidoreductases; Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase - metabolism; Procollagen-Proline Dioxygenase - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)91023-9

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.