75 



an analogous structure with phosphate at one end, an isoalloxazine 

 instead of the purine at the other, and a ribose instead of a ribo- 

 furanose in the middle. Only the function of riboflavine is, in a 

 way, the opposite of that of ATP. While the function of ATP is 

 to spend the E of -^P's wisely, the function of riboflavine is to 

 invest E in P's, taking part in oxidative phosphorylation and stabi- 

 lizing the energy released in this form. ATP accepts phosphates 

 from other phosphate acceptors in the form of a triphosphate 



OH 

 H H H H I 



CH2-C-C-C-C-O-P-OH 

 I H II 



I H H H R 1^ 



VO 



^^ 



(a) (6) 



Fig. 20. a: Riboflavine-5, -phosphate, oxidized, b: Same reduced. 



chain, then breaking down this chain, converting (as we sup- 

 posed) its (E) into an £* in the purine. The tentative hypoth- 

 esis thus suggests itself that riboflavine might do the same in the 

 opposite direction and fulfill its role by converting the £* gener- 

 ated by its oxido-reduction in its alloxazine into ^P's by building 

 up a triphosphate chain on its other end, the phosphates of which 

 it then passes on to other phosphate acceptors, keeping but one for 

 itself. 



As to the mechanism of these reactions we supposed that ATP 

 connected its two ends (on the enzyme) by forming a coordinative 

 metal complex between the active groups of its purine and the 

 triphosphate end. So, when studying ATP, our first question was 

 whether the formation of such a complex is sterically possible. If 

 there is the supposed analogy between ATP and riboflavine, then 

 we might ask likewise whether the opposite process is sterically 

 possible, whether the alloxazine could bind two phosphates as 

 metal complexes, then hitch them together and bind them to its 



