66 



UNITY AND DIVERSITY IN BIOCHEMISTRY 



(b) Glucose-6-phosphate {Rohison ester) — Although the existence of this 

 ester had been known since 1914 from experiments on yeast carried out by 

 Harden and Robison, it was not until 1931 that Robison and King suc- 

 ceeded in obtaining it in the pure state. 



{c) Glucose-l,6-diphosphate — This ester, which is a coenzyme in gly- 

 colysis, was isolated by Leloir from yeast after incubation with phosphate 

 and glucose. 



(d) Fructose-1 -phosphate (Robison ester) — Hydrolysis of fructose- 1, 

 6-diphosphate by phosphatases, gives equal amounts of fructose- 1- 

 phosphate and fructose-6-phosphate. Fructose-1 -phosphate has been 

 isolated from liver and been found in the intestine during the intestinal 

 absorption of fructose. 



(e) Fructose-6-phosphate (Neuberg ester) — Fructofuranose-6-phosphate 

 was first prepared by partial hydrolysis of fructose-1, 6-diphosphate and 

 later isolated from the products of alcoholic fermentation. In normal acid, 

 at 100°, the phosphate group in position 1 is split off about a dozen times 

 more rapidly than the group in position 6. 



(/) Fructose-l, 6-diphosphate (Harden and Young ester) — Fructofura- 

 nose-1, 6-diphosphate in alkaline solution (0-2N NaOH) at 100° liberates 

 the whole of its phosphate in three minutes. 



(g) Other phosphorylated sugars and their derivatives present in the 

 biosphere — Such compounds are galactose- 1 -phosphate, ribitol phosphate, 

 sedoheptulose phosphate, gluconic acid phosphoric ester, etc. 



(e) Pyridoxal-5-Phosphate and Pyridoxamine-5- Phosphate 



These are important coenzymes, the former in the decarboxylation of 

 amino acids, in transaminations, deamination of hydroxyaminoacids and in 

 the removal of sulphur from amino acids containing sulphur. 



O 



I! 



HO-P-OH 



6 c«o 



H,C 



OH 



^CH3 



Pyridoxal-5-phosphate 



o 



II 



HO-P-OH 



^ CH.NH, 



H2C 



OH 



l.,^^" 



Pyridoxamine-5-phosphate 



