Adaptation of an enzymatic cycling assay for NADP(H) measurement to the COBAS-FARA centrifugal analyzer

NADP(H) measurements by enzymatic amplification are described in which the interface step between cycling (glucose-6-phosphate and glutamic dehydrogenases) and indicator (6-phosphogluconic dehydrogenase) enzymes has been reconfigured, permitting the entire operation to run as a continuous assay on a centrifugal fast analyzer. This is accomplished by using the sequential load feature of the analyzer and incorporating either sodium dodecyl sulfate (SDS) or SDS and hydrogen peroxide as kill reagents to replace the thermal step (destruction of cycle enzymes by boiling). The ability of SDS to render a cycle inoperative during the run time of the indicator enzyme depends on the inherent resistivity and absolute amount of its enzyme proteins to this surfactant. Criteria used to judge the efficacy of a potential kill reagent are based on the sample blank time-response curve and the cycle product recovery by the indicator enzyme. Various other enzyme cycling systems which can be fitted to the centrifugal fast analyzer are highlighted.