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Correcting a potential defect in an enzymatic cycle for NADP.

C S Hintz, M M Chi, O H Lowry

    Analytical Biochemistry
    |January 1, 1983
    PubMed
    Summary

    Enzyme inactivation in NADP assays is prevented by maintaining a pH below 7.2. Other proteins in the reagent aid heat inactivation, solving a common issue in glucose-6-phosphate dehydrogenase assays.

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    Area of Science:

    • Biochemistry
    • Enzymology

    Background:

    • Enzymatic assays for NADP+ often utilize glucose-6-phosphate dehydrogenase (G6PD) from Leuconostoc mesenteroides.
    • Incomplete heat inactivation of G6PD can lead to assay interference and inaccurate results.
    • Previous studies have not fully elucidated the factors contributing to G6PD heat inactivation instability.

    Purpose of the Study:

    • To identify the cause of incomplete heat inactivation of Leuconostoc mesenteroides glucose-6-phosphate dehydrogenase.
    • To determine methods for completely inactivating the enzyme before the indicator step in NADP+ enzymatic cycles.
    • To optimize reagent composition for enhanced enzyme stability.

    Main Methods:

    • Investigated the effect of pH on the heat inactivation of glucose-6-phosphate dehydrogenase.
    • Assessed the influence of other protein components within the reagent on enzyme inactivation.
    • Performed enzymatic activity assays under varying pH conditions.

    Main Results:

    • A minor increase in pH was identified as the primary cause of incomplete heat inactivation.
    • The presence of other proteins in the reagent significantly enhanced the heat inactivation of G6PD.
    • Maintaining a pH below 7.2 completely resolved the enzyme inactivation issue.

    Conclusions:

    • Assay instability caused by incomplete G6PD heat inactivation can be overcome by strict pH control.
    • The formulation of the reagent, including auxiliary proteins, plays a crucial role in enzyme stability.
    • Optimizing pH is a simple yet effective strategy to ensure reliable enzymatic cycling for NADP+ determination.

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