BIOCHEMICAL STUDIES ON <i>d</i>-RIBOSE, WITH SPECIAL REFERENCE TO THE MECHANISM OF ABSORPTION OF SUGARS FROM INTESTINAL TRACT

J-STAGE

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1. d-Ribose was most sensitive, among pentoses, to chemical reactions; the sugar was most labile against the action of alkali, and it produced, upon distilling in the presence of mineral acid, furfural at the highest velocity. The yield of furfural was almost quantitative.<br> 2. The minimum quantity of ribose, which caused pentosuria upon the intravenous injection or the oral administration to rabbits, was 250mg. or 2gm. per kilogram of body weight respectively.<br> 3. The subcutaneous injection of ribose resulted in the increase of the quantity of the glycogen fraction in the livers of mice. The perfusion of the isolated livers of rabbits with the physiological saline solution containing ribose also raised the glycogen fraction in the livers.<br> 4. Ribose was absorbed from the intestinal tracts of rats which had been starved for 48 hours, at a distinctly higher rate than other pentoses. The relative rate of its absorption in the first hour was 74 when compared to that of glucose=100.<br> 5. The absorption of ribose from the intestinal loops of rats was also selective. The absorption was followed by the decrease of inorganic phosphate in the intestinal tract and by the increase of acid-soluble organic phosphate in the mucosa. This phosphoryla-tion was inhibited when poisoned with monoiodoacetate. 6. During the absorption from the whole digestive tract, as well as from the intestinal loop, every sugar was eliminated at a distinctly higher rate in the first quarter of an hour, followed by a lower and almost a constant rate. It was pointed out that the C o r i law was applicable only in the later period of the absorption.<br> 7. The selective absorption of ribose, glucose, galactose, and fructose, was accompanied by the increase of the glycogen-like substance in the intestinal mucosa of rats. This increase of the substance was more distinct in the sugar which was absorbed at a higher rate. The production curve of the substance rose to a maximum at an earlier stage in the sugar which was absorbed more rapidly, and then the curve tended to recede faster to the original value. The formation of the substance in the mucosa was strictly confined to the very place where the absorption took place. The formation of the substance disappeared when the selective absorption was inhibited by monoiodoacetate. The mechanism of the selective absorption of sugars has been discussed on the basis of these experimental findings, emphasis being given to the close connection between the selective absorption, phosphorylation and the production of the glycogen-like substance.<br> Expenses of this work were defrayed by Grants for the Advancement of Natural Science from the Department of Education.

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