Evidence for the presence of fatty acid binding protein in avian granulosa cells.

The existence of fatty acid binding protein in chicken ovarian granulosa cells was investigated using a fluorescent assay based on the ability of cis-parinaric acid to fluoresce as a result of its interaction with proteins. Cytosolic fractions were prepared from granulosa cells obtained from the first (F1), second (F2), and third (F3) largest preovulatory follicles as well as from a pool of small yellow follicles of the chicken ovary, and each fraction was incubated with different concentrations of cis-parinaric acid. Total fluorescence increased (but fluorescence per milligram protein decreased) as the quantity of cytosolic protein from all follicle types was increased. Cis-parinaric acid fluorescence (which was also dose-dependent) was observed within 2 sec and increased with time reaching a plateau at about 10 sec. It was greater (p < 0.001) in the cytosolic fraction from F3 and small yellow follicle groups compared with F2 and F1 groups. Arachidonic, palmitic, oleic and stearic acids attenuated the fluorescence in dose-dependent fashion in cytosol from all follicle types presumably by displacing cis-parinaric acid from protein. Whereas arachidonic acid was most effective in suppressing fluorescence in fractions from F1 follicles, arachidonic acid lost part of its suppressive potency in fractions from F3 or small yellow follicles, and in these fractions palmitic acid was the most potent suppressor of fluorescence. These results indicate the existence of fatty acid binding protein-like activity in chicken granulosa cells and demonstrate that its concentration is greatest in the immature follicles. This protein could play an important role in the transport of fatty acids within granulosa cells.