1.3- Bisphosphoglycerate dehydrogenase

FIGURE 16.10 Formation of a covalent intermediate in the glyceraldehyde-3-phos-phate dehydrogenase reaction. Nucleophilic attack by a cysteine —SH group forms a covalent acylcysteine intermediate. Following hydride transfer to NAD, nucleophilic attack by phosphate yields the product, 1,3-bisphosphoglycerate. 

A requirement for all fermentations is the existence of a mechanism for coupling ATP synthesis to the fermentation reactions. In the lactic acid and ethanol fermentations this coupling mechanism consists of the formation of the intermediate 1,3-bisphosphoglycerate by the glyceraldehyde 3-phosphate dehydrogenase (Fig. 10-3, step a). This intermediate contains parts of both the products ATP and lactate or ethanol. 

A V- - NAD+ Triosephosphate Isomerase y"— NADH Glyceraldehyde Phosphate Dehydrogenase 1,3-Bisphosphoglycerate A U -ADP... 

Step 6 involves the oxidation of D-glyceraldehyde 3-phosphate, accompanied by phosphorylation of the intermediate carboxylic acid, to produce D-l,3-bisphosphoglycerate. The enzyme is glyceral-dehyde-3-phosphate dehydrogenase. 

Glyceraldehyde 3-phosphate is oxidized by NAD+ and reacts with inorganic phosphate (Pi) to form 1,3-bisphosphoglycerate and NADH + H+. -Enzyme glyceraldehyde 3-phosphate dehydrogenase... 

A. Dihydroxyacetone phosphate (compound I) is isomerized to glyceraldehyde 3-phosphate and converted in a series of steps to pyruvate (compound II). One of the reactions requires glyceraldehyde 3-phosphate dehydrogenase, which utilizes inorganic phosphate and produces one NADH. In the conversion of one 1,3-bisphosphoglycerate to one pyruvate, two ATP are produced. A mutase is not required. 

---