The synthesis of L-ascorbic acid in the rat from D-glucuronolactone and L-gulonolactone.

Previous studies have shown that the intact carbon chain of glucose is utilized for the synthesis of L-ascorbic acid in the rat (l-3). Evidence for this precursor relationship came from experiments in which the administration of carbon land carbon 6-labeled glucose tracers resulted in the urinary excretion of n-ascorbic acid labeled predominantly in carbon 6 and carbon 1, respectively. Although these earlier studies were carried out in rats receiving Chloretone to increase their normal rate of L-ascorbic acid biosynthesis (4), recent results have shown that glucose is also a precursor of n-ascorbic acid in rats not treated with this drug (5). Two possible pathways for the biosynthesis of n-ascorbic acid from glucose in rats have been investigated. One, involving L-sorbose as an intermediate, was ruled out in a previous isotopic study (6). The other pathway involving n-glucuronolactone and n-gulonolactone as intermediates is shown in the accompanying scheme.