J. Biochem, 1992, Vol. 112, No. 6 750-755
© 1992 Japanese Biochemical Society
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Inhibition of Sarcoplasmic Reticulum Ca2+-ATPase by 2,5-Di(Tert-Butyl)-1,4-Benzohydroquinon1
Department of Molecular Physiology, National Cardiovascular Center Research Institute Suits, Osaka 565
We characterized the interaction of 2,5-di(tert-butyl)-l,4-benzohydroquinone (tBuBHQ) with the sarcoplasmic reticulum (SR) Ca2+-ATPase from rabbit fast-twitch skeletal and canine cardiac muscles by examining the effect of this agent on the ATPase reaction. tBuBHQ at less than 10 µM inhibited ATP hydrolysis by both isoforms of Ca2+-ATPase by up to 80 and 90%, respectively. The half maximal inhibition of these enzymes was observed at about 1.6 pM tBuBHQ. Thus, this agent potently inhibits the fast-twitch skeletal and slow-twitch skeletal/cardiac isoformas of SR Ca2+-ATPase. tBuBHQ at 6–10 µM inhibited the rate of decomposition of the phosphoenzyme intermediate (EP), measured as a ratio between ATPase activity and the EP level in the steady state, by 36–40%. It also inhibited formation of EP by decreasing the rate of Ca2+ binding to the Ca2+-deficient, nonphosphorylated enzyme to about 1/8 of the control value. These results indicate that tBuBHQ has at least two sites of action in the reaction sequence for the SR Ca2+-ATPase.
1This study was supported by a research grant for cardiovascular diseases (A2–1) from the Ministry of Health and Welfare of Japan.
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