首页 | 本学科首页   官方微博 | 高级检索  
   检索      


Proton transport by gastric membrane vesicles
Authors:H Chang  G Saccomani  E Rabon  R Schackmann  G Sachs
Institution:Laboratory of Membrane Biology, University of Alabama in Birmingham, Birmingham, Ala. 35294 U.S.A.
Abstract:A highly purified membrane fraction was derived from hog gastric mucosa by a combination of differential and density gradient centrifugation and free flow electrophoresis. This final fraction was 35-fold enriched with respect to cation activated ouabain-insensitive ATPase. Antibody against this fraction was shown to be bound to the luminal surface of the gastric glands. The addition of ATP to this fraction or the density gradient fraction resulted in H+ uptake into an osmotically sensitive space. The apparent Km for ATP was 1.7 · 10?4 M in the absence of a K+ gradient similar to that found for ATPase activity. The reaction is specific for ATP and requires cation in the sequence K+ > Rb+ > Cs+ > Na+ > Li+ and is inhibited by ATPase inhibitors such as N,N′-dicylclohexylcarbodiimide. Maximal H+ uptake occurs with an outward K+ gradient but the minimal apparent KA is found in the absence of a K+ gradient. The pH optimum for H+ uptake is between 5.8 and 6.2 which corresponds to the pH range for phosphorylation of the enzyme, but is considerably less than the pH maximum of the K+ dependent dephosphorylation. In the presence of an inward K? gradient, protonophores such as tetrachlorsalicylanilide only partially abolish the H+ gradient but valinomycin dissipates 75% of the gradient, and nigericin abolishes the gradient. The vesicles therefore have a low K+ conductance but a measurable H+ conductance, hence a K+ gradient can produce an H+ gradient in the presence of valinomycin. The uptake and spontaneous leak of H+ are temperature sensitive skin with a similar transition temperature. Ultraviolet irradiation inactivates ATPase and proton transport at the same rate, approximately at twice the rate of p-nitrophenylphosphatase inactivation. It is concluded that H+ uptake by these vesicles is probably due to a dimeric (H+ + K+)-ATPase and is probably non-electrogenic.
Keywords:DCCD  N  To whom correspondence should be addressed  
本文献已被 ScienceDirect 等数据库收录!
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号