Correcting a potential defect in an enzymatic cycle for NADP

An enzymatic cycle for NADP which uses as one of its enzymes glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides has occasionally caused trouble due to failure to completely heat-kill this enzyme before the indicator step. It was found that a very small increase in pH was the cause of this. It was also found that the other two proteins present in the reagent greatly increase heat inactivation of the enzyme. The inactivation problem is completely overcome by keeping the pH below 7.2.