LUIS F. LELOIR 



glucose-l,6-diphosphate + mannose-1 -phosphate ;= 



mannose-l,6-diphosphate + glucose-6-phosphate (1) 

 followed by the catalytic action of mannose diphosphate : 



mannose-1 56-diphosphate + mannose-1 -phosphate v ^ 



mannose-1, 6-diphosphate + mannose-6-phosphate (2) 



The first step was proved (13) by detecting the formation 

 of mannose diphosphate on incubation of mannose-1 -phosphate, 

 glucose diphosphate, and the enzyme. Furthermore, it has been 

 observed (21) that synthetic mannose diphosphate will activate 

 the transformation of either glucose- 1 -phosphate or mannose- 1- 

 phosphate. Moreover, similar events take place with the ribose 

 esters. Glucose diphosphate activates the transformation of the 

 1- into the 5-phosphate, and the formation of ribose- 1,5-diphos- 

 phate has been detected (12). With acetylglucosamine-1 -phos- 

 phate the problem is more complex. Muscle phosphoglucomu- 

 tase does not act on this ester, but extracts can be obtained from 

 a mold {Neurospora) which catalyze the conversion of the 1- into 

 the 6-phosphate. These extracts have been separated in dif- 

 ferent fractions (23) in which the ratio of activity, phospho- 

 glucomutase/phosphoacetylglucosaminomutase, varies from 300 

 to 0.3, that is, as if at least two difTerent enzymes were involved. 

 But in either fraction the transformation of the 1 -esters is acti- 

 vated by glucose-1, 6-diphosphate, and this fact can be taken as 

 an indication that both glucose and acetylglucosamine esters fit 

 the active group of one of the enzymes. 



Such an overlapping in the action of these enzymes suggests 

 that there may be a genetic relationship between them, and that 

 their lack of specificity may be the result of a gradual evolution- 

 ary change. 



If we were to let the imagination loose at the risk of being 

 laughed at by more learned colleagues, we might reason some- 

 what as follows. 



Adaptation experiments suggest that the substrate is in some 

 manner involved in the formation of the corresponding enzyme. 

 It is then possible that if the substrate were changed slightly, the 



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