Functional effect of hydrogen peroxide on the sarcoplasmic reticulum membrane: uncoupling and irreversible inhibition of the Ca2+-ATPase protein |
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Authors: | Sánchez Sonia Fernández-Belda Francisco Soler Fernando |
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Institution: | Departamento de Bioquímica y Biología Molecular A, Facultad de Veterinaria, Universidad de Murcia en Espinardo, 30071 Espinardo, Murcia, Spain. |
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Abstract: | The chemical treatment of sarcoplasmic reticulum vesicles with H2O2 affects both Ca2+ transport and the hydrolytic activity supported by the Ca2+-ATPase protein. Ca2+ transport was much more sensitive to inhibition than ATPase activity and the decrease in Ca2+ transport was not the result of an increase in membrane permeability. The Ca2+/Pi uncoupling can be attributed to the own catalytic mechanism of the enzyme. Under conditions of high uncoupling, Ca2+ binding to the transport sites was barely affected and accumulation of phosphorylated species during the enzyme cycling gave almost maximal levels. These are features defining intramolecular uncoupling mediated by a phosphorylated form of the enzyme. Severe inhibition of the hydrolytic activity was observed when higher peroxide concentrations and leaky vesicles were used. These experimental conditions diminished maximal Ca2+ binding and the steady-state phosphoenzyme level. The low hydrolytic activity can be ascribed to a decrease in the rate of enzyme dephosphorylation. |
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Keywords: | Hydrogen peroxide Oxidative damage Ca2+-ATPase protein Uncoupling mechanism Sarcoplasmic reticulum Skeletal muscle |
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