CHEMISTRY OF RIBOSE AND DEOXYRIBOSE 37 



carboxamkle riboside. '^'^ Moreover Korii et a/.'^* working with purified 

 beef liver nucleoside phosphorylase obtained some evidence of reaction 

 between ribose-1 -phosphate and adenine. This result differs from that ob- 

 tained by Kalckar working with rat liver nucleoside phosphorylase. 



An accumulation of evidence supports the designation of the pentose 

 phosphate as ribose-1 -phosphate. It is nonreducing and readily hydrolyzed 

 by acid to equimolecular quantities of phosphate ions and pentose. The 

 extreme acid lability supports a glycosidic phosphate ester linkage and 

 indeed the substance is sufficiently acid-labile to lose its phosphate group 

 by hydrolysis at the acidity employed in some of the methods available 

 for phosphate estimation. The ester is somewhat more acid-labile than 

 phosphocreatine but less so than acetyl phosphate. For example in 0.5 N 

 sulfuric acid the half-time for splitting for phosphocreatine, acetyl phos- 

 phate and ribose-1-phosphate is 4 miiuites, 30-40 seconds and 2.5 minutes, 

 respectively. Further support for the glycosidic linkage is afforded by the 

 enzymic conversion of the phosphate ester to purine ribosides which also 

 have a linkage to C-1 of the sugar moiety. The stereochemical configuration 

 of the phosphate ester linkage is unknown, but it is probably of the jS-type. 

 Natural nucleosides are considered to be /S-furanosides,'"*^' '^^ and, if nucleo- 

 side phosphorylase (like polysaccharide phosphorylase) produces no in- 

 versioUj^"" the ribose-1 -phosphate should also be of the /3-furanose type. The 

 furanose structure for the lactol ring is supported by the observation' ^'^ 

 that synthetic ribopyranose-1 -phosphate is inactive as a substrate for 

 nucleoside phosphorylase. 



Ribose-1 -phosphate can be converted enzymically by mutase action into 

 ribose-5-phosphate. [Cf. Glock, Chapter 22.] Klenow and Larsen'^"' have 

 shown that phosphoglucomutase preparations,^"^' ^"^ acting in conjunction 

 with glucose- 1 ,6-diphosphate (or possibly ribose-1 ,5-diphosphate) as 

 coenzyme, will bring about this change. The ratio of the enzymic activities 

 of phosphoglucomutase : phosphoribomutase was about 100:1. Reports by 

 Wajzer and Baron-"* indicate that liver contains an enzyme capable of 

 transforming ribose-1 -phosphate into the -5-phosphate. 



(2) Rihose-2- and -3 -'phosphates. The location of the phosphate residue 

 in the first pair of isomeric nucleotides discovered and isolated by Cohn^^ 

 (adenylic acids "a" and "b") has generally been regarded as at the 2'- and 



»9» E. D. Korn, F. C. Charalampous, and J. M. Buchanan, J. Am. Chem. Soc. 75, 3610 



(1953). 

 '99 J. Davoll, B. Lythgoe, and A. R. Todd, J. Chem. Soc. 1946, 833. 

 ^oo Mildred Cohn, J. Biol. Chem. 180, 771 (1949). 



^"^ Hans Klenow and B. Larsen, Arch. Biochem. and Biophys. 37, 488 (1952). 

 ^o^ V. A. Najjar, ./. Biol. Chem. 175, 281 (1948). 

 2« E. W. Sutherland, J. Biol. Chem. 180, 1279 (1949). 

 20^ J. Wajzer and Frangoise Baron, Bull. soc. chim. biol. 31, 750 (1949). 



