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 5.8 x 10(-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 1.6 x 10(-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 E-1 state in the presence of ATP and Mg2+ and forms the complex hinesol-H+ . E-1-ATP or hinesol . E-1-P, blocking the conformational change to the E-2 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. BIOCHEM PHARMACOL 59;7:861-886, 2000. (C) 2000 Elsevier Science Inc.