Inhibition of H+,K+ -ATPase by hinesol, a major component of So-jutsu, by interaction with enzyme in the E1 state.
Hinesol, a major component of the crude drug "So-jutsu" (Atractylodis Lanceae Rhizoma), strongly inhibited H+,K+-ATPase activity with a IC50 value of 5.8x10(-5) M. It also inhibited Na+,K+-ATPase, Mg2+-ATPase, Ca2+-ATPase, and H+-ATPase activities, although the inhibition rate was lower. No effects on alkaline or acid phosphatase activities were observed. The mechanism by which hinesol inhibited H+,K+-ATPase activity was studied in detail. The inhibition was uncompetitive with respect to ATP, and it increased as the Mg2+ concentration was raised, whereas it was not affected by the K+ concentration. The activity of K+-dependent p-nitrophenyl phosphatase (K+-pNPPase), a partial reaction of H+,K+-ATPase, was inhibited by hinesol noncompetitively with respect to pNPP (IC50 value of 1.6x10(-4) M), and competitively with respect to K+, whereas it was not affected by the Mg2+ concentration. These results suggest that hinesol is a relatively specific inhibitor of H+,K+-ATPase. It appears that hinesol reacts with enzyme in the E1 state in the presence of ATP and Mg2+ and forms the complex hinesol-H+ E1-ATP or hinesol x E1-P, blocking the conformational change to the E2 state. Furthermore, hinesol enhanced the inhibitory effect of omeprazole on H+,K+-ATPase, and the inhibitory site of hinesol was different from that of omeprazole. The effect of So-jutsu as an anti-gastric ulcer agent may be ascribed to the inhibitory effect of hinesol on H+,K+-ATPase activity.
Satoh
K
K
Department of Toxicology, The Tokyo Metropolitan Research Laboratory of Public Health, Japan. sato@tokyo-eiken.go.jp
Nagai
F
F
Kano
I
I
D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D004365:Drugs, Chinese Herbal / Q000737:chemistry*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D066298:In Vitro Techniques; D008024:Ligands; D008516:Medicine, Chinese Traditional; D009853:Omeprazole / Q000494:pharmacology; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D054328:Proton Pump Inhibitors; D012717:Sesquiterpenes; D013141:Spiro Compounds / Q000494:pharmacology*; D013552:Swine
D004365:Drugs, Chinese Herbal; D004791:Enzyme Inhibitors; D008024:Ligands; D054328:Proton Pump Inhibitors; D012717:Sesquiterpenes; D013141:Spiro Compounds; C065858:hinesol; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D000251:Adenosine Triphosphatases; D009853:Omeprazole