Specific inhibition of Na+,K(+)-ATPase activity by atractylon, a major component of byaku-jutsu, by interaction with enzyme in the E2 state.
Atractylon, a major component of the crude drug "Byaku-jutsu" (rhizomes of Atractylodes japonica), strongly inhibited Na+,K(+)-ATPase activity with an I50 value of 8.9 x 10(-6) M. It also inhibited Mg(2+)-ATPase, H+,K(+)-ATPase, H(+)-ATPase and Ca(2+)-ATPase activities, but less potently. No effects on alkaline and acid phosphatase activities were observed. The inhibition of Na+,K(+)-ATPase activity by atractylon was noncompetitive with respect to ATP and was greater with increasing K+ concentration, whereas it was not affected by Na+ concentration. The activity of K(+)-dependent p-nitrophenyl phosphatase, a partial reaction of Na+,K(+)-ATPase, was inhibited noncompetitively with respect to substrate (I50 value of 1.8 x 10(-5) M), and the inhibition rate was independent of the K+ concentration. Furthermore, atractylon increased the Ki value for Na+ from 130 to 190 mM, but did not alter the Ki value for ATP. Inhibition of the phosphoenzyme formation by atractylon was greater at 0.1 M than at 1 M NaCl. K(+)-dependent dephosphorylation (E2-P to K.E2) was inhibited by atractylon, whereas ADP-sensitive (Na.E1-P to Na.E1) and non-specific dephosphorylation steps were not affected. These results suggest that atractylon, a specific inhibitor of Na+,K(+)-ATPase, interacts with enzyme in the E2 state and inhibits the reaction step from E2-P to K.E2.
Satoh
K
K
Department of Toxicology, Tokyo Metropolitan Research Laboratory of Public Health, Japan.
Nagai
F
F
Ushiyama
K
K
Kano
I
I
D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors; D000818:Animals; D005753:Gastric Mucosa / Q000201:enzymology; D006736:Horses; D007668:Kidney / Q000201:enzymology; D008516:Medicine, Chinese Traditional; D010766:Phosphorylation / Q000187:drug effects; D010946:Plants, Medicinal; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D012717:Sesquiterpenes / Q000494:pharmacology*; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000302:isolation & purification
D012717:Sesquiterpenes; D012965:Sodium Chloride; D011189:Potassium Chloride; C046196:atractylon; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase