Calcium transport by pigeon erythrocyte membrane vesicles

Membrane vesicles from pigeon erythrocytes show a rapid, ATP-dependent accumulation of 45Ca2+.Ca2+ accumulation ratios greater than or approximately equal to 10(4) are readily attained. For ATP-dependent Ca2+ uptake, V is 1.5 mmol.1(-1).min(-1) at 27 degrees C (approx. 0.9 nmol.mg-1 protein.min-1), [Ca2+]1/2 is 0.18 microM, [ATP]1/2 is 30--60 microM, the Ca2+ uptake rate depends on [Ca2+]2 and the dependence of uptake rate on ATP concentration implies strong ATP-ATP cooperativity. The Arrhenius activation energy is 19.1 +/- 1.4 kcal/mol and the pH optimum is approx. 6.9.