Koshiishi I, Mamura Y, Imanari T
Faculty of Pharmaceutical Sciences, Chiba University, Japan.
Biochim Biophys Acta. 1998 Feb 2;1379(2):257-63. doi: 10.1016/s0304-4165(97)00106-2.
The half-life of dehydroascorbate (DHA) in human plasma is only a few minutes. This DHA disappearance is caused by a cleavage of lactone ring. Similarly, when DHA was incubated in Dulbecco's modified Eagle's medium (D-MEM), which stood in atmosphere of 5% CO2-95% air, the rapid transformation of DHA into 2,3-diketogulonate (2,3-DKG) is also observed. These observations suggest that both human plasma and D-MEM contain a common component, which promotes the hydrolysis of DHA. In the present study, this component was identified to be bicarbonate which acts as a general base catalyst. Direct evidence for this mechanism was obtained as follows: (1) significant hydrolysis of DHA in the bicarbonate-free D-MEM (pH 7.40) was not observed; (2) hydrolysis of DHA in Tris-HCl buffer at constant pH (7.4) increases with increasing bicarbonate concentration; and (3) significant hydrolysis of DHA in the decarbonated ultrafiltrate of plasma was not observed. These results suggest that DHA hydrolysis may be controlled by the variation of CO2 pressure in circulating blood.
脱氢抗坏血酸（DHA）在人体血浆中的半衰期仅为几分钟。DHA的这种消失是由内酯环的裂解引起的。同样，当DHA在置于5%二氧化碳-95%空气气氛中的杜氏改良 Eagle 培养基（D-MEM）中孵育时，也观察到DHA迅速转化为2,3-二酮古洛糖酸（2,3-DKG）。这些观察结果表明，人体血浆和D-MEM都含有一种共同成分，该成分促进DHA的水解。在本研究中，该成分被鉴定为作为一般碱催化剂的碳酸氢盐。该机制的直接证据如下：（1）在无碳酸氢盐的D-MEM（pH 7.40）中未观察到DHA的显著水解；（2）在恒定pH（7.4）的Tris-HCl缓冲液中，DHA的水解随碳酸氢盐浓度的增加而增加；（3）在血浆的脱碳酸超滤物中未观察到DHA的显著水解。这些结果表明，DHA水解可能受循环血液中二氧化碳压力变化的控制。
