MODES OF LINKAGE BY COVALENT BONDS 



65 



(d) Phosphor ylated Sugars 



1. Ribose phosphates 



The ribose phosphate normally present in cells is ^-D-ribose-1 -phosphate; 

 it is very acid-labile. Desoxyribose-1 -phosphate is even more unstable in 

 acid solution; at pH 4-0 at room temperature, it is 50% hydrolysed in 15 

 minutes. It is hydrolysed in the course of estimations of "inorganic phos- 

 phate" and is consequently often measured as such. 



\ 



O H 



\ / 



C 



HC 



HCOH O 



HCOH 



PO3H, 



\ 

 O 



H 



\ / 

 C — 



CH2 



HCOH 



HC 



O 



CH.OH 



^-D-ribose-l -phosphate 



CH2OH 

 Desoxyribose- 1 -phosphate 



2. Hexose phosphates 



(a) oc-D-glucose-\-phosphate [Cori ester) — This ester is reducing and is 

 stable to alkali, on hydrolysis glucose is liberated. 



CH.OH 



O H 



O - PO,H, 



OH 



Glucose-1 -phosphate 

 Cori ester 



CH;,0 - POjH, 



OH 



Glucose-6-phosphate 

 Robison ester 



HiOjP-OHjC 



CHjOH 



OH 



Fructose-6-phosphate 

 Neuberg ester 



HjOaP - OH;.C 



CH.OP03H, 



OH 



Fructose-1 ,6-diphosphate 

 Harden and Young ester 



F 



