The sarcoplasmic reticulum Ca2+-ATPase, pumps 2 mol Ca2+ out of sarcomeres per mol ATP hydrolyzed.(a) Given the following steady-state concentrations and a membrane potential of 65 mV (inside negative), calculate ΔG for the following activetransport process at 37 °C and pH = 7.4:2Ca2+(in) + ATP + H2O → 2Ca2+(out) + ADP + Pi + H+ATP = 2.6 mM, ADP = 210 μM, Pi = 5.1 mM, Ca2+(in) = 32 mM,Ca2+(out) = 2.2 mM(b) In active muscle the pH can drop below 7.4. Is the reaction above moreor less favorable under these conditions?(c) The activity of the Ca2+-ATPase is regulated reversibly under normalconditions to maintain homeostatic concentrations of Ca2+ inside thesarcomere. However, in a rare genetic disorder, irreversible activation ofthe Ca2+ -ATPase can occur. Assuming 37 °C, pH = 7.4, and the steadystate concentrations for ATP, ADP Pi, and Ca2 +(out) given in part (a),calculate the minimum [Ca2 +] inside a sarcomere that has irreversibly activated Ca2 +-ATPase (i.e., the Ca2 +-ATPase activity is always “on”)
The sarcoplasmic reticulum Ca2+-ATPase, pumps 2 mol Ca2+ out of sarcomeres per mol ATP hydrolyzed.
(a) Given the following steady-state concentrations and a membrane potential of 65 mV (inside negative), calculate ΔG for the following active
transport process at 37 °C and pH = 7.4:
2Ca2+(in) + ATP + H2O → 2Ca2+(out) + ADP + Pi + H+
ATP = 2.6 mM, ADP = 210 μM, Pi = 5.1 mM, Ca2+(in) = 32 mM,Ca2+(out) = 2.2 mM
(b) In active muscle the pH can drop below 7.4. Is the reaction above more
or less favorable under these conditions?
(c) The activity of the Ca2+-ATPase is regulated reversibly under normal
conditions to maintain homeostatic concentrations of Ca2+ inside thesarcomere. However, in a rare genetic disorder, irreversible activation of
the Ca2+ -ATPase can occur. Assuming 37 °C, pH = 7.4, and the steadystate concentrations for ATP, ADP Pi, and Ca2 +(out) given in part (a),calculate the minimum [Ca2 +] inside a sarcomere that has irreversibly activated Ca2 +-ATPase (i.e., the Ca2 +-ATPase activity is always “on”)
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