Inhibition of choline acetyltransferase activity by serum albumin modified with octanoic acid and other fatty acids.

In this study, we examined the effect of fatty acids on choline acetyltransferase (ChAT) activity. ChAT is unstable in a solution of low protein concentration, so serum albumin (BSA) is usually added to stabilize the enzyme. However, we found that ChAT from bovine caudate nucleus rapidly lost its activity when diluted with a buffer containing commercial preparations of BSA. This effect was caused by octanoic acid, which was found in the gas chromatography/mass spectrometry system of lipid extract in commercial BSAs. The inhibition of ChAT activity by octanoic acid depended on the concentrations of the octanoic acid and of the albumin. We also found that ChAT activity was decreased by some long-chain fatty acids, arachidonic acid having exhibited the strongest effect. The extent to which arachidonic acid inhibited ChAT activity depended on the molar ratio of arachidonic acid and albumin, rather than upon the concentration of arachidonic acid. The effect of octanoic acid and arachidonic acid on ChAT activity appeared to increase in the presence of albumin.