The inhibitors thapsigargin and 2,5‐di(tert‐butyl)‐1,4‐benzohydroquinone favour the E2 form of the Ca2+, Mg2+‐ATPase

摘要

>2,5-Di(tert-butyl)-1,4-benzohydroquinone has been shown to inhibit the Ca2+, Mg2+-ATPase of sarcoplasmic reticulum with an affinity of 0.4 μM. It has been shown to shift the E2-E1 equilibrium for the ATPase towards E2, as shown previously for the inhibitor thapsigargin. The shift towards E2 results in a decrease in affinity for Ca2+, as also observed for thapsigargin. A marked decrease in the rate of the E2-E1 transition is observed for both BHQ and thapsigargin. A decrease in the equilibrium level of phosphorylation by P_i and of the steady-state lever of phosphorylation by ATP are consistent with a decrease in the equilibrium constant for phosphorylation by P_i and an increase in the rate of dephosphorylation.