抄録
For further clarification of the role of L-ascorbic acid (AsA) in the prolyl 4-hydroxylase reaction, the specificity of AsA for the decarboxylation of α-ketoglutarate (KGA) was studied using various reductants including AsA and its structural analogs. Decarboxylation of KGA was not observed in the absence of AsA. Erythorbic acid (ErA) was found to be as effective as AsA, and D-ascorbic acid was almost as effective as AsA in the reaction. Whereas, thiol compounds showed a very slight accelerating effect on the decarboxylation of KGA. L-Scorbamic acid (SCA) or erythroscorbamic acid (ErS), at a concentration 10-fold greater than AsA, showed a decarboxylation level of 40-45% that of AsA. Furthermore, in the presence of AsA, the pHdependence and concentration effect on the decarboxylation of KGA were different from those in the presence of SCA. Moreover, the Lineweaver-Burk plot of the inhibition by SCA of AsA showed that the mode of interaction of SCA with AsA may be apparently noncompetitive. From these results, it is suggested that, due to its planar ring system with an endiol group, AsA is a specifically suitable reducing compound for inducing the decarboxylation of KGA in the enzyme reaction.
