Stoichiometry of calcium transport by sarcoplasmic reticulum: utilization of p-nitrophenylphosphate as an energy donor]

We have studied, under different conditions and through the hydrolysis of p-nitrophenylphosphate, the stoechiometry of the active transport of calcium by sarcoplasmic reticulum. According to a minimal kinetic model, it is possible to explain the variation of the coupling factor n(t) during the calcium accumulation in absence of precipitating agent. Under the described experimental conditions, at the beginning of the experiment, the coupling factor's value is slightly above 2.