The biosynthesis of glucuronic acid from 1-C14-glucose.

Although many classes of substances found in the animal organism have been suggested as possible biological precursors of glucuronic acid (l), recent research has narrowed the number of these possibilities to two, namely hexoses (2,3) and trioses (4, 5). Various experimental techniques, including isotopic tracers, have been used in the effort to choose between these alternatives, but invariably the results have been equivocal. It occurred to us that a study of the incorporation of an unsymmetrically labeled hexose would provide a definitive answer to this question. The present communication describes an experiment in which 1-C4-glucose was administered to a menthol-fed rabbit; menthyl glucuronide, isolated from the urine of the animal, was found to be labeled predominantly in the 1st carbon atom of the glucuronic acid moiety. It is concluded that a 6carbon unit is the immediate precursor of glucuronic acid in the rabbit.