The metabolism of D-ribose in man.

Previously thought to be primarily a structural component of nucleic acids, the pentose, D-ribose, in the form of the ester, ribose 5-phosphate, has now been shown to be an important intermediate in the pentose phosphate pathway of glucose metabolism. The sequence of the reactions of this pathway has been summarized by Horecker and Mehler (1) and Wood (2), and surveys of its significance in various mammalian tissues have been reported (3-6). Naito (7) has investigated the glycogenic effect of ribose after its injection into mice and rabbits, and Herrmann and Hickman (8) have described the utilization of ribose by beef cornea. Horecker, Gibbs, Klenow, and Smyrniatis (9) have demonstrated the conversion of ribose to hexose with rat liver homogenates and Katz, Abraham, Hill, and Chaikoff (10), incubating ribose 1-C14 with rat liver slices, observed the formation of glucose with a pattern of labeling that was predictable from the reactions of the pentose phosphate pathway. Similar findings have been reported by Hiatt (11), studying the in vivo conversion of labeled ribose to glucose in the mouse. Recently Agranoff and Brady (12) have isolated and purified from calf liver an enzyme, ribokinase, which is capable of phosphorylating ribose to ribose 5-phosphate, thus permitting the sugar to enter the pentose phosphate pathway. The entrance of ribose into the pathway, and the sequence of its conversion to glucose are shown in Figure 1. Since ribose appears to be of importance in mammalian metabolism, we have undertaken a study of certain phases of ribose metabolism in man. This paper presents data concerning the fate of ribose after its intravenous administration in both unlabeled and C14 labeled form to both normal and diabetic subjects. Preliminary results of these studies have been published (13), as well as a report of the hypoglycemia induced by ribose infusion (14). Previous publications (15, 16) from this laboratory have described the physiologic disposition in man of the related pentoses D-Xylose, Dand L-arabinose, and D-lyxose, as well as the effects of insulin on the blood levels of these sugars.