ATP/ADP exchange activity of gastric |
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Authors: | E Rabon G Sachs S Mårdh B Wallmark |
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Institution: | Laboratory of Membrane Biology, University of Alabama in Birmingham, Birmingham, AL 35294 U.S.A. |
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Abstract: | The ATP/ADP exchange is shown to be a partial reaction of the by the absence of measurable nucleoside diphosphokinase activity and the insensitivity of the reaction to , -di(adenosine-5′) pentaphosphate, a myokinase inhibitor. The exchange demonstrates an absolute requirement for Mg2+ and is optimal at an ADP/ATP ratio of 2. The high ATP concentration () required for maximal exchange is interpreted as evidence for the involvement of a low affinity form of nucleotide site. The ATP/ADP exchange is regarded as evidence for an ADP-sensitive form of the phosphoenzyme. In native enzyme, pre-steady state kinetics show that the formation of the phosphoenzyme is partially sensitive to ADP while modification of the enzyme by pretreatment with 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) in the absence of Mg2+ results in a steady-state phosphoenzyme population, a component of which is ADP sensitive. The ATP/ADP exchange reaction can be either stimulated or inhibited by the presence of K+ as a function of pH and Mg2+. |
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Keywords: | ATP-ADP exchange (Stomach) CDTA DTNB 5 5′-dithiobis (2-nitrobenzoic acid) Pipes 1 4-piperazine-diethanesulfonic acid |
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