The metabolic fate of C14 labeled pentoses in man.

The role of pentoses in intermediary metabolism has received much attention within the past few years. The phosphate esters of D-ribose, D-ribulose and D-xylulose have been identified as key intermediates in the pentose phosphate pathway of glucose metabolism in both plant and mammalian tissue (1). More recently, another alternate pathway of glucose dissimilation, the uronic acid pathway, has been described in which L-Xylulose, xylitol and D-xylulose are intermediates (2). Several pentoses have been identified in normal urine: the aldopentoses xylose, arabinose and ribose (3, 4) and the ketopentoses D-ribulose and L-xylulose (5). Large quantities of the latter sugar are excreted in the disease essential pentosuria (6, 7), which appears to be due to a defect in the further conversion of L-xylulOse to the sugar alcohol xylitol (8). In addition to L-xylulOse Touster and Harwell (9) have also reported the isolation of L-arabitol from the urine of pentosuric subjects. Because of increasing awareness of the biological importance of the pentoses, certain aspects of pentose metabolism in man have been investigated in this laboratory. Previous reports have described the physiological disposition of large quantities of infused pentoses (10), the effect of insulin on blood levels of infused pentoses (11) as well as studies of the metabolism of D-ribose (12). This paper reports some observations on the fate of C14 labeled D-xylOse, D-lyxose, D-arabinose and L-arabinose administered in trace quantities intravenously to normal human subjects. Some of the previously published data (12) on C14 ribose metabolism are included for purposes of comparison.