Features of inhibition of glycerol-3-phosphate oxidase activity of liver mitochondria by palmitic acid in the presence of ATP and tert-butylhydroperoxide

Abstract

The effect of palmitic acid on glycerol-3-phosphate oxidation, i.e., on the glycerol-3-phosphate oxidase (GP oxidase) activity of liver mitochondria was investigated in the presence and absence of ATP, as well as under conditions of tert-butylhydroperoxide (TBH)-induced oxidative stress. It was found that palmitic and lauric acids inhibit GP oxidase activity of deenergized liver mitochondria formally in the competitive manner. In this case lauric acid, which is less hydrophobic than palmitic acid, inhibits GP oxidase activity of mitochondria significantly weaker. It is noted that the competitive inhibition of mitochondrial GP oxidase activity by these saturated fatty acids may be related to their ability, as amphiphilic compounds, to increase the negative charge density on the outer surface of the inner mitochondrial membrane. It is shown that ATP at a concentration of 2 mM eliminates the ability of palmitic acid to inhibit GP oxidase activity of mitochondria. This effect of ATP is not observed in the presence of F O F 1-ATP synthase inhibitor oligomycin. Apparently, in the case of vector transport of H+ from the matrix to the intermembrane space of mitochondria induced by ATP hydrolysis there is occurs protonation of palmitic acid anions on the outer surface of the inner membrane and subsequent movement of its neutral molecules to the inner monolayer of the inner membrane. It was found that TBH at a concentration of 300 µM in the presence of ATP and palmitic acid inhibits their GP oxidase activity formally in the competitive manner without significant effect on ATPase activity of liver mitochondria. Thiourea antioxidant eliminates this effect of TBH. It is assumed that TBH-induced oxidative stress in the case of ATP-energized mitochondria results in an increase in transport rate of palmitic acid anions from the inner monolayer of the inner membrane to its outer monolayer. This, in turn, is accompanied by an increase in the density of negative charges on the outer surface of the inner mitochondrial membrane and inhibition of GP oxidase activity of liver mitochondrial formally in the competitive manner.