THE METABOLIC FATE OF C14 LABELED PENTOSES IN MAN

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Abstract
Carbon 14 labeled D-xylose, D and L-arabinose and D-ribose were administered intravenously to normal human subjects and the quantity of Cl4 excreted as C14O2 and that excreted in the urine ascertained. The rates of disappearance of Cl4 from blood were also determined. It was found that a significant amount of all of the pentoses studied except L-arabinose was catabolized to Cl4O2. Whereas D-xylose, D-arabinose and D-lyxose conversion to Cl4()2 was 16, 19 and 14 per cent of the administered dose, D-ribose conversion was 48% in 6 hours. Much of the label appeared in the urine during the 24 hour period after infusion. C14 in urine after D-xylose, D-lyxose, D-arabinose, L-arabinose and D-ribose infusion was 35, 72, 57,85 and 10% of the dose respectively. Paper chromatography of the urine revealed only a small part of this C14 to be unmetabolized pentose except in the case of D-ribose. The 10% excretion of the latter C14 appeared to be entirely unaltered sugar. These findings suggest the presence of as yet unidentified metabolites of pentose in the urine.