Interaction of β-eudesmol with Na +K +-ATPase: inhibition of K +-pNPPase activity

Abstract

The effect of β-eudesmol, one of the major components in So-jutsu (Atractylodis Lanceae Rhizoma), on K +-dependent p-nitrophenyl phosphatase (K +pNPPase) activity was studied. It inhibited K +-pNPPase activity with an I 50 value of 4.1 × 10 −4. The inhibition rate decreased as the K + concentration was increased, whereas greater inhibition was observed with high concentrations of either Na + or ATP. The K i, values for Na + in the presence of 0, 0.1 and 1 mM ATP were 140, 260 and 310 mM, respectively, but with the addition of β-eudesmol, these values decreased to 90 mM regardless of the ATP concentration. This study on K +-pNPPase activity supports the conclusion obtained from the study on Na +,K +-ATPase activity (Satoh K et al., Biochem Pharmacol 44: 373–378, 1992) that is, β-eudesMol interacts with enzyme in the Na·E 1 form and inhibits the reaction step Na·E i→ Na·E 1P. Furthermore, in the study of the effects of K + and β-eudesmol on K +-pNPPase activity, it was confirmed that β-eudesmol prevents the conformational change of Na·E 1 → K·E 2.