Glucose-6-phosphate dehydrogenase GPDase

GPDase (D-glucose-6-phosphate NADP+ oxidoreductase EC 1.1.1.49) is frequently used for AM-type El A, particularly for substances in sera (Table 10.19). This enzyme is widely distributed (Keller, 1971 Lohr and Waller, 1974). However, unlike its mammalian 

Applications of glucose-6-phosphate dehydrogenase and detection range (/ig/ml) in homogeneous EIA 

Catalytic properties and assay of glucose-6-phosphate dehydrogenase The reaction catalyzed by the bacterial GPDase 

The unit activity is defined as the amount of enzyme which oxidizes 1 /rmole of glucose-6-phosphate to 6-phospho-D-gluconate per min in the presence of NADP+ at pH 7.8 and 30 C (specific activity up to about 400 U/mg). If NAD+ is used as coenzyme, activity increases by a factor of 1.8. 

Mg + stimulates the enzyme up to 10 mM but inhibits its activity at higher concentrations. Other bivalent cations are often inhibitory. Another important inhibitor is phosphate, though NADP+ may reverse to a certain extent this inhibition (Glaser and Brown, 1955). There is a rather pronounced pH dependence of the L. mesenteroides GPDase activity (Ldhr and Waller, 1974), namely 7.8. 

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The previously discussed enzymes may all be used for solid-phase AM assays. For homogeneous AM-type EIA, lysozyme, malate dehy-rogenase (MDase), glucose-6-phosphate dehydrogenase (GPDase), and ribonuclease A (RNase A), are used in addition to BGase. 

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