Fatty acid-binding to erythrocyte ghost membranes and transmembrane movement.

Palmitate binding to human erythrocyte ghost membranes has been investigated with ghost preparations suspended in 0.2% albumin solutions. Free unbound palmitate in the extracellular water phase was measured in equilibrium studies using albumin-filled acid loaded ghosts as small semipermeable bags. The apparent dissociation constant of binding to the membrane is 13.5 nM and the binding capacity 19 nmoles per 7.2 x 10(9) cells. The 0 degree C exchange efflux kinetics of palmitate from albumin-filled ghosts is described by a model, which provides estimates of the rate constant of membrane transfer, k3 = 0.024 s-1, independent of the molar ratio of palmitate to albumin (v) and of a mean dissociation rate constant of the palmitate-albumin complex, k1 = 0.0015 s-1 at v 0.2, allowing for a heterogeneity of the palmitate binding to albumin. The values of a third kinetically determined v dependent model constant, Q, the ratio of palmitate bound to the membrane inner surface to palmitate on intracellular albumin, are not different from the Q values obtained by equilibrium experiments. The temperature dependences of k1 and k3 in the interval 0 degrees C to 15 degrees C give activation energies of 96 and 103 kJ/mole, respectively. The 0 degrees C exchange efflux increases about 2 fold in response to a rise of pH from 6 to 9. The results suggest a carrier mediated palmitate flux at low v with a Vmax about 2 pmoles min-1 cm-2 at 0 degrees C pH 7.3.