Different arachidonate and palmitate binding capacities of the human red cell membrane

Human red cell membrane bindings of arachidonate and palmitate at pH 7.3 are investigated at temperatures between 0 and 38°C by equilibrating ghosts with the long-chain fatty acids bound to bovine serum albumin in molar ratios (v) within the physiological range (<1.7). Linearized relations of ghost uptakes and fatty acid monomer concentrations in buffer provide estimates of the binding capacities and corresponding equilibrium dissociation constants (K _dm ). The temperature-independent arachidonate binding capacity, 5.5 ± 0.5 nmol g^–1 packed ghosts, is approximately fivefold smaller than that of palmitate, 26.6 ± 2.0 nmol g^–1. While K _dm of arachidonate binding 5.1 ± 0.5 nm is temperature independent, K _dm of palmitate increases with temperature from 3.7 nm at 0°C to 12.7 nm at 38°C.The large difference in binding capacities suggests the presence of at least two different fatty acid binding domains in human red cell membranes.