期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 276, 期 27, 页码 25078-25087出版社
ELSEVIER
DOI: 10.1074/jbc.M103318200
关键词
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Sarcoplasmic reticulum vesicles of rabbit skeletal muscle accumulate Ca2+ at the expense of ATP hydrolysis, The heat released during the hydrolysis of each ATP molecule varies depending on whether or not a Ca2+ gradient is formed across the vesicle membrane. After Ca2+ accumulation, a part of the Ca2+-ATPase activity is not coupled with Ca2+ transport (Yu, X,, and Inesi, G, (1995) J, Biol, Chem. 270, 4361-4367), I now show that both the heat produced during substrate hydrolysis and the uncoupled ATPase activity vary depending on the ADP/ATP ratio in the medium. With a low ratio, the Ca2+ transport is exothermic, and the formation of the gradient increases the amount of heat produced during the hydrolysis of each ATP molecule cleaved. With a high ADP/ATP ratio, the Ca2+ transport is endothermic, and formation of a gradient increased the amount of heat absorbed from the medium. Heat is absorbed from the medium when the Ca2+ efflux is coupled with the synthesis of ATP (5.7 kcal/mol of ATP), When there is no ATP synthesis, the Ca2+ efflux is exothermic (14-16 kcal/Ca2+ mol). It is concluded that in the presence of a low ADP concentration the uncoupled ATPase activity is the dominant route of heat production, With a high ADP/ATP ratio, the uncoupled ATPase activity is abolished, and the Ca2+ transport is endothermic, The possible correlation of these findings with thermogenesis and anoxia is discussed.
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