A high-performance liquid chromatographic method for the assay of Na+, K+-adenosine triphosphatase inhibition

A new method for the assay of Na+, K+-adenosine triphosphatase (Na+, K+-ATPase) inhibition has been devised involving the determination of enzymatically produced adenosine diphosphate (ADP) and unchanged adenosine triphosphate (ATP) by high-performance liquid chromatography (HPLC). The substrate, ATP, was incubated with the enzyme preparation in the presence of an inhibitor. The incubation mixture was filtered through a membrane filter, and ADP and ATP in the filtrate were separated by (HPLC). The inhibitory effect of a cardiac steroid on the enzymic reaction was estimated by measuring the peak area ratio of ADP to ADP plus ATP on the chromatogram. The proposed assay method has proved to be satisfactory with respects to simplicity, sensitivity, and reproducibility.