234 ^- ^^- KALCKAR VOL. 4 (1950) 



i-phospho group in ribose-1-phosphate. This selective trait with regard to purines will 

 be discussed a little later. With regard to the sugar component the furanoid structure 

 of the sugar seems to be imperative for the reaction. Thus, pyranose-ribose-1-phosphate 

 (synthesized by chemical means by Todd and Lythgoe) was practically inactive in the 

 enzyme test as was a-glucose-1-phosphate. Although the furanoid structure of the pentose 

 seems to be essential, other changes in the sugar molecule seem to affect the enzymatic 

 exchange much less. Klein had already observed that liver and spleen nucleosidase 

 catalyse the splitting of purine desoxyribosides just as well as purine ribosides. We have 

 found too that nucleoside phosphorylases fractionated by various means catalyse the 

 phosphorolysis of purine desoxyribosides as well as the purine riboside^' '. If we assume 

 that the enzymatic catalysis of the two types of nucleosides is due to the same enzyme 

 and there is good evidence for such an assumption, the substitution of an OH group by 

 a H at carbon no. 2 seems to be unessential for the activity of the liver nucleoside 

 phosphorylase. 



ENZYMATIC SYNTHESIS OF DESOXYRIBO-NUCLEOSIDES 



It was tempting to analyse a little more closely the phosphorolysis of desoxyri- 

 bosides, and if possible perform an enzymatic synthesis of nucleosides belonging to the 

 desoxyribose series. Friedkin who joined our group here in Copenhagen as a research 

 visitor participated in this project and undertook a closer analysis of some of the com- 

 ponents of the system. Guanine desoxyriboside was isolated and subjected to an enzym- 

 atic phosphorolysis analogous to that used for ribosides. After removal of the inorganic 

 phosphate the Lowry-Lopez phosphate analysis was performed in order to disclose the 

 the presence of a highly acid-labile ester. The outcome was entirely negative. The failure 

 to detect any ester formation by this method could be due to the fact that the 1-ester 

 formed in this case was more stable than ribose-1-phosphate. The other alternative 

 was that the 1-ester was even more acid-labile than ribose-1-phosphate. We were inclined 

 towards the latter possibility. This turned out to be correct. If free phosphate and ester 

 phosphate are estimated separately, using precipitation of the true inorganic phosphate 

 by means of ammoniacal ammonium-magnesium sulphate it is possible to detect the 

 formation of a desoxyribose phosphoric ester. This new ester was found to undergo 

 rapid hydrolysis in an acetate buffer of pn 4 at room temperature. Friedkin found that 

 50% of the desoxyribose phosphate ester was spHt in 11 minutes at 25° at pn 4- This 

 is presumably the most acid-labile phosphoric ester yet described. It has been possible 

 to show that this ester can act as a precursor for desoxynucleoside synthesis in vitro. 

 The quantitative assay of the desoxyribose ester is under preparation and it can there- 

 fore only be stated that if hypoxanthine is incubated with liver nucleoside phosphorylase 

 in the presence of a moderate excess of the desoxyribose ester (but no inorganic phos- 

 phate) more than 50% of the hypoxanthine is incorporated with the desoxysugar. The 

 enzymatic formation of a desoxynucleoside was further substantiated by Hoff- 

 Jorgensen using the microbiological technique^' ^. A proper estimation of the amount 

 of aldose present before and after mild hydrolysis of the new desoxyribose ester is under 

 preparation. It is felt most likely that the new ester is an analogue of ribose-1-phosphate, 

 i.e., a desoxyribose-1-phosphate. 



Recently Manson and Lampen^ in Cori's department have prepared an enzyme 

 from thymus gland which brings about a splitting of hypoxanthine desoxyriboside 



References p. 23^. 



