Glycerol-3-phosphate dehydrogenase, reaction catalyzed

The secondary alcohol group of glycerol-3-phosphate is then oxidized by NAD to a ketone. The enzyme that catalyzes this reaction is called glycerol phosphate dehydrogenase. Recall that a dehydrogenase is an enzyme that oxidizes its... 

Step 3 of Figure 29.3 Alcohol Oxidation The /3-hydroxyacyl CoA from step 2 is oxidized to a /3-ketoacyl CoA in a reaction catalyzed by one of a family of L-3-hydroxyacyl-CoA dehydrogenases, which differ in substrate specificity according to the chain length of the acyl group. As in the oxidation of sn-glycerol 3-phosphate to dihydroxyacetone phosphate mentioned at the end of Section 29.2, this alcohol oxidation requires NAD+ as a coenzyme and yields reduced NADH/H+ as by-product. Deprotonation of the hydroxyl group is carried out by a histidine residue at the active site. 

Glycerol-3-phosphate dehydrogenase (NAD ) [EC 1.1.1.8] catalyzes the reaction of xn-glycerol 3-phosphate with NAD+ to produce glycerone phosphate (or, dihydroxyacetone phosphate) and NADH. 1,2-Propanediol phosphate and glycerone sulfate can also act as substrates, having a weaker affinity. 

In fact, the enzyme glycerol 3-phosphate dehydrogenase catalyzes this reaction (see Fig. 21-17). 

All assay methods are based on the forward ALD-catalyzed reaction. Both photometric fixed-time and continuous-monitoring procedures have been developed. In the analytical approach on which all the commonly used procedures and kits are based, the ALD reaction is coupled with two other enzyme reactions. Triosephosphate isomerase (EC 5.3.1.1) is added to ensure rapid conversion of all GLAP to DAP. Glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) is added to reduce the DAP to glycerol-3-phosphate, with NADH acting as hydrogen donor. The decrease in NADH concentration is then measured. 

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