Tsao C S, Young M
Linus Pauling Institute of Science and Medicine, Palo Alto, California 94306.
In Vivo. 1990 May-Jun;4(3):167-9.
The effect of exogenous ascorbic acid intake on enzymatic formation of ascorbic acid in mice has been studied. After the mice were on diets containing ascorbic acid for two months, the rates of ascorbic acid formation in mouse liver homogenates were measured in vitro using glucuronolactone and gulonolactone as substrate in their respective reaction systems. Exogenous ascorbic acid intake (1, 5 or 8% in the diet) was able to reduce activities of ascorbic acid synthesizing enzymes in mouse liver in either the glucuronolactone or gulonolactone system. The control mechanism for reaction of glucuronolactone to produce ascorbic acid is not stereospecific because large amounts of dietary erythorbic acid, a stereoisomer of ascorbic acid, could also reduce the rate of ascorbic acid formation when glucuronolactone was used as substrate. However, the regulation of ascorbic acid synthesis using gulonolactone as a precursor was apparently stereospecific. Dietary glucose or xylitol had no effect on activities of ascorbic acid synthesizing enzymes.
已研究了外源性摄入抗坏血酸对小鼠体内抗坏血酸酶促合成的影响。小鼠在含抗坏血酸的日粮中饲养两个月后，在体外分别以葡萄糖醛酸内酯和古洛糖酸内酯作为底物，测定小鼠肝脏匀浆中抗坏血酸的合成速率。外源性抗坏血酸摄入量（日粮中为1%、5%或8%）能够降低葡萄糖醛酸内酯或古洛糖酸内酯系统中小鼠肝脏中抗坏血酸合成酶的活性。葡萄糖醛酸内酯生成抗坏血酸反应的调控机制并非立体特异性的，因为大量日粮中的异抗坏血酸（抗坏血酸的立体异构体）在以葡萄糖醛酸内酯为底物时，也能降低抗坏血酸的合成速率。然而，以古洛糖酸内酯作为前体的抗坏血酸合成调控显然是立体特异性的。日粮中的葡萄糖或木糖醇对抗坏血酸合成酶的活性没有影响。
