STUDIES ON THE MECHANISM OF ACTION OF A80915A, A SEMI-NAPHTHOQUINONE NATURAL PRODUCT, AS AN INHIBITOR OF GASTRIC (H+-K+)-ATPASE
STUDIES ON THE MECHANISM OF ACTION OF A80915A, A SEMI-NAPHTHOQUINONE NATURAL PRODUCT, AS AN INHIBITOR OF GASTRIC (H+-K+)-ATPASE
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DOI：
10.1016/0006-2952(91)90603-3
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发表时间：
1991-10-24
影响因子：
5.8
通讯作者：
MYNDERSE, JS
中科院分区：
文献类型：
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作者：
DANTZIG, AH;MINOR, PL;MYNDERSE, JS
蓝链霉菌(Streptomyces Aculeolatus)产生的半萘醌天然产物A80915A对胃(H+-K+)-ATPase有很强的抑制作用，该酶负责胃酸分泌。用从猪胃底粘膜制备的酶，通过钾刺激的ATP或对-硝基苯酚磷酸水解酶来测定酶的活性。ATPase和对-硝基苯基磷酸酶的IC50均为2-3-mU-M，呈浓度依赖性抑制。Hill图表明该酶与A80915A有两个结合位点。抑制作用不受还原剂二硫苏糖醇的影响，表明酶的巯基不参与。随着药物浓度的增加，酶孵育30分钟，然后稀释10倍，IC50没有改变，表明A80915A不会共价修饰酶。酶与3.8mU-M A80915A共孵育后，抑制作用呈时间依赖性。20 mM的钠、锂、胆碱和40 mM的蔗糖对抑制作用无明显影响，而20 mM的钾、铋和铵的存在可显著减缓抑制作用。抑制程度受加钾顺序和加药顺序的影响。综上所述，这些研究表明，A80915A的抑制依赖于胃(H+-K+)-ATPase的构象，而钾通过将酶转化为药物结合部位不容易到达的构象来减缓抑制速度。A80915A的作用模式与两种质子泵抑制剂奥美拉唑和SCH 28080不同。
A semi-naphthoquinone natural product, A80915A, produced by Streptomyces aculeolatus was found to be a potent inhibitor of gastric (H+-K+)-ATPase, the enzyme responsible for acid secretion in the stomach. Enzyme activity was measured by potassium-stimulated hydrolysis of ATP or p-nitrophenolphosphate with enzyme prepared from the stomach fundic mucosa of pigs. Concentration-dependent inhibition was observed with an IC50 of about 2-3-mu-M for both ATPase and p-nitrophenylphosphatase. A Hill plot indicated that the enzyme has two binding sites for A80915A. Inhibition was not affected by the presence of the reducing agent dithiothreitol, indicating a lack of involvement of enzyme sulfhydryl groups. A 30-min incubation of enzyme with increasing drug concentrations followed by a 10-fold dilution did not alter the IC50 indicating that A80915A does not covalently modify the enzyme. Coincubation of enzyme with 3.8-mu-M A80915A resulted in time-dependent inhibition. The rate of inhibition was slowed significantly by the presence of 20 mM potassium, rubidium and ammonium but not by 20 mM sodium, lithium and choline, or by 40 mM sucrose. The level of inhibition was influenced by the order of addition of potassium and drug to the enzyme. Taken together, these studies indicate that inhibition by A80915A is dependent on the conformation of gastric (H+-K+)-ATPase and that potassium slows the rate of inhibition by converting the enzyme to a conformation where the drug binding site is not as accessible. The mode of action of A80915A is distinct from that of two well characterized proton pump inhibitors, omeprazole and SCH 28080.