PHOSPHORYLATION OF CARBOHYDRATES 179 



self -perpetuating. The phosphorylation of glucose enables it to un- 

 dergo oxidation by way of triosephosphate and pyruvate, and this 

 oxidation causes further phosphorylation of glucose, thus providing 

 new substrate for oxidation and so on. 



During recovery of muscle from work, oxidative energy is also 

 converted into phosphate bond energy; that is, the phosphocreatine 

 which breaks down during muscular contraction is reformed largely 

 at the expense of oxidation, and the phosphorylation of glucose 

 which is supplied by the blood stream provides the necessary sub- 

 strate for the resynthesis of the glycogen lost during contraction. 



Intramolecular Migration of Phosphate Groups 



The first enzymatic reaction of this type was described by Meyer- 

 hof and Kiessling (9), namely, the conversion of glyceric acid-3- to 

 glyceric acid-2-phosphate. This reaction was shown to be reversible, 

 and the assumption that one is dealing with an intramolecular mi- 

 gration of the phosphate group was confirmed by the use of radio- 

 active phosphorus. 



Another reaction of this type is the conversion of glucose-1- to 

 glucose-6-phosphate. This reaction was at first regarded as irre- 

 versible, but more recent work has shovsni that it can be reversed 

 under suitable experimental conditions; that is, glucose-6-phosphate 

 can be converted to glucose-1-phosphate and then to glycogen (10). 

 To study the equilibrium of this reaction it was necessary to separate 

 the enzyme which catalyzes this reaction from interfering enzymes 

 which upset the equilibrium by acting either on glucose-1- or glu- 

 cose-6-phosphate. With such a purified enzyme preparation 94 per 

 cent of added glucose-1-phosphate is converted to an ester which was 

 isolated and identified as glucose-6-phosphate. Fructose-6-phosphate 

 was absent, because Lohmann's enzyme (11), which catalyzes the 

 reversible reaction between glucose-6- and fructose-6-phosphate, 

 had been removed. Conversely, when pure glucose-6-phosphate was 

 added to the enzyme, 6 per cent of glucose-1-phosphate was formed; 

 that is, the same equilibrium was reached from either side. From 

 the equihbrium constant (K = 15.7 at pH 7 and 25° C.) it may be 

 calculated that the change in standard free energy amounts to about 

 —1600 calories. 



When barium ions and phosphorylase were added to this system, 

 glucose-6-phosphate was converted to glycogen. As shown in Table 

 2, the position of the equilibrium of the second reaction is unfavor- 

 able for glycogen synthesis, because only a smaU amount of glucose- 



