Glyceraldehyde-3-phosphate, oxidative phosphorylation

Glyceraldehyde-3-phosphate dehydrogenase is a homotetramer that carries out the oxidative phosphorylation of glyceraldehyde-3-phosphate into 1,3-bisphos- phoglycerate. During this reaction NADH is formed. Each subunit of the enzyme consists of two domains and has an NAD+ binding site. The N-terminal domain anchors the adenosine portion of the cofactor while the nicotinamide portion is involved in the catalytic reaction at the C-terminal domain. T brucei... 

Glyceraldehyde 3-phosphate dehydrogenase, a tetrameric enzyme of Mr 150 000 containing four identical chains, catalyzes the reversible oxidative phosphorylation of glyceraldehyde 3-phosphate to 1,3-diphosphoglycerate, using NAD+ as a coenzyme (equation 16.11). 

In fact, the glyceraldehyde 3-phosphate dehydrogenase reaction also consumes NADH, equivalent to two molecules of NADH for each molecule of glucose synthesized. Since each cytosolic NADH would normally be used to generate approximately two ATP molecules via the glycerol 3-phosphate shuttle and oxidative phosphorylation (see Topic L2), this is equivalent to the input of another four ATPs per glucose synthesized. 

Arsenic, in its arsenate (AsO ") form prevents the se quential transformation of glyceraldehyde 3-P to 3-P glycerate (D-5). Arsenate resembles phosphate and can substitute for it in oxidative phosphorylation, and also attach to glyceraldehyde 3-P, in place of phosphate. The resultant unstable arsenate compound does change to the normal end result, 3-P-glycerate, but without the normal production of an ATP. This is poisonous. 

Fig. 1.6. An example of the reaction which yields energy by the oxidation of an organic compound by an organic compound in the alcohol fermentation. Circled numbers 1, glyceraldehyde-3-phosphate dehydrogenase (phosphorylating) 2, alcohol dehydrogenase 3, phosphoglycerate kinase.

Tables 13-la and 13-lb list only the most important categories of enzyme classes (E.C. s). Some enzymes that are involved in reactions at phosphorus are hidden in other classes. For example glyceraldehyde-3-phosphate dehydrogenase, which catalyses the oxidative phosphorylation of glyceraldehyde-3-phosphate to 1,3-diphospho-glycerate, is classified under E.C. 1.2.1.12 and 1.2.1.13. Neither the name of the enzyme nor its IUB-classification, gives information about the phosphorylating step. Identifying enzymes potentially useful in synthesis that have been ambiguously classified is difficult for those outside of biochemistry because no complete reference is available connecting enzymatic activity with synthetic applicability.

---