Inhibition of Na+,K(+)-ATPase activity by beta-eudesmol, a major component of atractylodis lanceae rhizoma, due to the interaction with enzyme in the Na.E1 state.
beta-Eudesmol, a major component of the crude drug "So-jutsu" (Atractylodis Lanceae Rhizoma), inhibited Na+, K(+)-ATPase activity most strongly among the various kinds of phosphatases examined. It also inhibited Ca(2+)-ATPase and H+, K(+)-ATPase, but to a lesser extent. Its effect on Mg(2+)-ATPase was minute. No effects on H(+)-ATPase or alkaline and acid phosphatase activities were observed. The effects of beta-eudesmol on horse kidney Na+, K(+)-ATPase were studied in detail, and the following results were obtained: (1) beta-eudesmol inhibited the Na+, K(+)-ATPase activity with an I50 value of 1.6 x 10(-4) M. The mode of its inhibition was uncompetitive with respect to ATP; (2) it prevented the stimulation of enzyme activity by Na+. The inhibition gradually increased in accord with the increase of Na+ concentration, and it was constant when Na+ was higher than 6.3 mM; (3) it did not alter the K+ concentration necessary for half-maximal activation (K0.5 for K+); and (4) it inhibited the enzyme activity with a mode of action different from ouabain. Phosphorylation of enzyme with [gamma-32P]ATP was inhibited by beta-eudesmol with an I50 of 1.4 x 10(-4) M. The inhibition was greater in 1 M NaCl than in 0.1 M NaCl. It had no effects on dephosphorylation steps, i.e. none of the non-specific, the ADP-sensitive (Na.E1-P----Na.E1) and the K(+)-dependent (E2-P----K.E2) dephosphorylation processes were affected. These results suggest that beta-eudesmol, a relatively specific inhibitor of Na+, K(+)-ATPase, interacts with the enzyme in the Na.E1 form and inhibits the reaction step Na.E1----Na.E1-P.[1]References
- Inhibition of Na+,K(+)-ATPase activity by beta-eudesmol, a major component of atractylodis lanceae rhizoma, due to the interaction with enzyme in the Na.E1 state. Satoh, K., Nagai, F., Ushiyama, K., Yasuda, I., Akiyama, K., Kano, I. Biochem. Pharmacol. (1992) [Pubmed]
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