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.
Satoh
K
K
Department of Toxicology, Tokyo Metropolitan Research Laboratory of Public Health, Japan.
Nagai
F
F
Ushiyama
K
K
Yasuda
I
I
Akiyama
K
K
Kano
I
I
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D017506:H(+)-K(+)-Exchanging ATPase; D006736:Horses; D007668:Kidney / Q000187:drug effects* / Q000201:enzymology; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D045787:Sesquiterpenes, Eudesmane; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects*; D013270:Stomach / Q000187:drug effects; D013729:Terpenes / Q000302:isolation & purification / Q000494:pharmacology*
D045787:Sesquiterpenes, Eudesmane; D013729:Terpenes; D012965:Sodium Chloride; C051082:beta-eudesmol; D011189:Potassium Chloride; D010744:Phosphoric Monoester Hydrolases; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase