Peroxisomal fatty acid oxidation as detected by H2O2 production in intact perfused rat liver

Abstract

H2O2 formation associated with the metabolism of added fatty acids was quantitatively determined in isolated Hb-free perfused rat liver (nonrecirculating system) by 2 different methods. Organ spectrophotometry of catalase Compound I was used to detect H2O2 formation by steady-state titration with added hydrogen donor, methanol or by comparison of fatty acid responses with those of the calibration compound, urate. In the use of the peroxidatic reaction of catalase, [14C]methanol was added as hydrogen donor at an optimal concentration of 1 mM in the presence of 0.2 mM-L-methionine and 14CO2 production rates were determined. The yield of H2O2 formation, expressed as the rate of H2O2 formation in relation to the rate of fatty-acid supply, was < 1.0 in all cases, indicating that, regardless of chain length, < 1 acetyl unit was formed/mol of added fatty acid by the peroxisomal system. In particular, the standard substrate used with isolated peroxisomal preparations (C16:0 fatty acid) gave low yield (close to zero). Long-chainmonounsaturated fatty acids exhibit a relatively high yield of H2O2 formation. The hypolipidemic agent bezafibrate led to slightly increased yields for most of the acids tested, but the yield with oleate was decreased to 1/2 the original yield. In the intact isolated perfused rat liver the assayable capacity for peroxisomal .beta.-oxidation is evidently used to only a minor degree. The observed rates of H2O2 production with fatty acids can account for a considerable share of the endogenous H2O2 production found in the intact animal.