The Possible Significance of d-Xyloketose (Urine Pentose) in Normal Metabolism.

Abstract

The author 1 has pointed out that pentosuria is hardly likely to be a disorder of carbohydrate metabolism. The amount excreted is always small and is, apparently, unaffected by the administration of large quantities of glucose or galactose. Since the excretion of pentose is diminished in fasting, 2 it would seem that the most likely source is protein. The pentose may be the result of an abnormal metabolic sequence or an intermediate in normal metabolism, which is not further oxidized.

The experiment reported in this paper was designed to throw some light upon this question. It is intended to repeat and to extend the work in various directions; but circumstances preclude the immediate continuance of the work.

The p-bromphenylhydrazone of the pentose was prepared by a modification of the method employed by Levene and LaForge. 3 It melted at 127-8° and decomposed at 165°. In a 1% solution in alcohol, the rotation was -1.87° shortly after preparation and +2.43° after 24 hours. 7.20 gm. of this compound were decomposed with benzaldehyde, as described by Levene and La Forge. The filtrate from the benzaldehyde p-bromphenylhydrazone was extracted with ether and then evaporated, in vacuo, to 100 cc. In a 1. dm. tube, the rotation was 1.18°. Since the calculated yield of pentose was 3.39 gm, [α]²² _d = 34.8° The glucose equivalent of 1 gm. of pentose. calculated from the p-bromphenylhydrazone was 1.25 gm. by Sumner's method, 5 1.45 gm. by the NaOH-picrateacetone method 6 and 1.18 gm. by the Na₂CO₃-picrate method. 7

This solution was injected into a young female dog, weighing 5.6 k., kept on a diet of 100 gm. beef heart, 16 gm. cracker meal, 16 cc. maize oil, 6 gm. bone-ash and 200 cc. water. There were 4 injections of 20 cc. and a fifth one of 10 cc., at intervals of approximately 2 hours. Calculated from the amount of hydrazone taken, the total amount of pentose injected was 3.05 gm. By Sumner's method, this showed a reducing action equivalent to that of 3.80 gm. glucose. The increase in the sugar content of the urine was equivalent to about 6% of the amount injected. A few days later, the animal received a similar series of injections of l-xylose. About 60% appeared in the urine. Another control experiment with glucose, gave, as was expected, no increase in the excretion of sugar.