Comparison between oleic acid and docosahexaenoic acid binding to interphotoreceptor retinoid-binding protein

Interphotoreceptor retinoid-binding protein (IRBP), which binds retinoids and fatty acids, is the major soluble protein in the interphotoreceptor matrix (IPM) but its role remains ambiguous. Using competitive fluorescence and tryptophan-quenching assays we found oleic acid and other cis-monounsaturated fatty acids bind much more strongly than does docosahexaenoic acid to bovine IRBP. IPM’s fatty acid composition was determined: it was richer in oleic acid than either the retinal pigment epithelium or rod outer segments. This may imply oleic acid has a key role in the balance and transport of retinoids and fatty acids in the retina.