Stearic acid desaturation in rat liver microsomes: stimulation by fatty acid binding protein.

A soluble protein (Mr = 12,000) showing the characteristics of fatty acid binding protein is partially purified from rat liver cytosol (15-fold on the basis of its affinity for oleic acid) using ammonium sulphate precipitation. More oleate than stearate is removed from liver microsomes incubated with similar amounts of both fatty acids and the protein, indicating that it has a higher affinity for oleic than for stearic acid. When added to microsomes, a fraction enriched in this protein stimulates stearic acid desaturation. Such an effect is abolished if the protein is pre-saturated with oleic acid. It is suggested that the stimulation of stearic acid desaturation by fatty acid binding protein may involve a selective removal of the product, oleic acid, from the microsomal membranes.