Abstract
d-Glucofuranosiduronolactone conjugates, namely, semicarbazone, oxime, cyanohydrin, and thioacetal of d-glucurono-1,4-lactone, were converted to l-ascorbic acid by an enzyme system present in rat, goat, or rabbit liver microsomes. Guinea pig liver microsomes were ineffective. Neither methyl- d-glucofuranosiduronolactone nor any glucopyranosiduronic acid conjugates examined were converted into l-ascorbic acid. Methods of preparation and properties of d-glucurono-1,4-lactone semicarbazone and d-glucurono-1,4-lactone oxime have been described and a tentative mechanism of enzymic reduction of the conjugates into l-gulono-1,4-lactone has been suggested. A conjugate of d-glucurono-1,4-lactone and imidazole, which is a substrate for the microsomal enzyme leading to synthesis of l-ascorbic acid, has been identified in the urine of rat treated with chloretone, barbital, and 1,2-benzanthracene. It has been indicated that the enhanced synthesis of l-ascorbic acid after administration of various drugs and toxic chemical compounds is due to the induced formation of this endogenous substrate.
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