Enzymatic formation of ascorbic acid in liver homogenate of mice fed dietary ascorbic acid

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.