The content of long-chain free fatty acids and their effect on energy transduction in chromaffin granule ghosts.

Highly purified chromaffin granule ghosts contain about 100 (89.1-110.2, n = 8) nmol of long-chain free fatty acids/mg of protein. About 40% of the fatty acids were mono- and polyunsaturated, of which arachidonate accounted for approximately 20%. Incubation with fatty acid-free bovine serum albumin selectively depleted the ghosts of unsaturated fatty acids. The effect of a series of long-chain fatty acids on energy coupling was studied in resealed chromaffin granule ghosts energized by MgATP. Their effectiveness in inhibiting the generation of the transmembrane proton concentration gradient and transmembrane potential was found to be correlated with their chain length and degree of unsaturation, all-cis-5,8,11,14-icosatetraenoate (arachidonate) and all-cis-5,8,11,14,-17-icosapentaenoate being most effective. Arachidonate was also found to dissipate an artificially generated pH gradient. Treatment of chromaffin granule ghosts with bovine serum albumin increased the transmembrane proton concentration gradient that could be generated by MgATP. This enhanced response to MgATP is presumably due to the removal of free fatty acids from the ghosts. Considering the potency of arachidonate and other unsaturated fatty acids, as well as their high endogenous content, these "uncoupling agents" should be accounted for when isolated chromaffin granules are used for in vitro studies on energy coupling.