TRIOSE PHOSPHATE OXIDATION 127 



enzyme. Consequently this particular step in the breakdown 

 process has three results: 



1. The oxidation of glyceraldehyde-phosphate to phospho- 

 glyceric acid. 



2. The formation of reduced coenzyme I as H-donator. 



3. The uptake of inorganic phosphate and its synthesis 

 into ATP. 



Phosphoglyceromutase now catalyses the transfer of the 

 phosphate group from the 3-position in glyceric acid to the 

 2-position, and water is removed from 2-phosphoglyceric 

 acid under the action of enolase. Phospho-enol-pyruvic acid 

 is produced which can lose its phosphate by transfer to 

 adenylic acid or adenosine-di-phosphate with the formation of 

 pyruvic acid and the regeneration of ATP. The phosphoryla- 

 tion of glucose to hexosediphosphate involves the dephosphory- 

 lation of two molecules of ATP, while the further breakdown of 

 each molecule of glyceraldehyde-phosphate regenerates two 

 molecules of ATP. 



In muscle, pyruvic acid is reduced to lactic acid by lactic 

 dehydrogenase working in reverse and utilising the reduced 

 coenzyme I as H-donator. The oxidation of glyceraldehyde- 

 phosphate and the reduction of pyruvic acid are thus linked by 

 coenzyme I acting as H-carrier between the two enzyme systems : 



CHO ■ COOH 



I Triosephosphate | ■RpdnopH 



CHOH -f Coenzyme I > CHOH + -^^^^^^^ 



I ^ Dehydrogenase | coenzyme I 



CH2OPO3H2 CH2OPO3H2 



CH3 ^ . CH3 -\^ 



' Rpflnrpd Lactic | 



*^0 +ccZ™eI ^ CHOH + Coenzyme I 



I -^ Dehj^drogenase I 



COOH COOH 



