The action of phloridzin and sugars on (Na+−K+)-Activated ATPase

Abstract

The action of phloridzin and simple sugars on the (Na⁺−K⁺)-activated ATPase obtained from rabbit kidney has been studied. Phloridzin 10⁻⁴to 10⁻³ m was found to inhibit the enzyme at Na⁺:K⁺ ratios less than optimal for enzyme activity, whereas stimulation was noted at Na⁺:K⁺ ratios greater than optimal for enzyme activity. Some sugars in concentrations of 0.1 to 0.5m were found to inhibit the (Na⁺−K⁺)-activated ATPase. The sugars and related compounds could be ranked according to decreasing inhibitory potency as: D-mannose>D-arabinose, D-xylose>L-xylose>D-glucose>fructose, L-arabinose>D-galactose, myo-inositol, mannitol=0. No stimulatory effect or interaction with K⁺ was found with these compounds. The action of these substances on the (Na⁺−K⁺)-activated ATPase suggests an interaction of actively transported sugars and sodium-potassium transport at the level of the sodium pump that may be important in the biological coupling of the two systems.