Influence of palmitate and oleate on the binding of warfarin to human serum albumin: stopped-flow studies.

The rate of transition from an unstable to a stable complex and the dependence of this on the number of fatty acid ligands present was determined for the binding of warfarin on human serum albumin. When oleate or palmitate was added in amounts up to 2:1 excess to human serum albumin solutions the measured rate constant for the transition (k2) was increased in comparison with fatty acid free albumin. When the fatty acid concentration is further increased, k2 decreases. When the fatty acid level is 2 to 3 mol per mol albumin, the affinity constant (KA) is higher than for fatty acid free solutions. With higher ratios the value for KA is reduced. According to the observed changes in kinetic parameters, the binding of warfarin is apparently affected allosterically. A reduced plasma protein binding of coumarins should be expected when fatty acid levels are raised over a prolonged period.