Changes in lipid metabolizing enzymes of hepatic subcellular fractions from rats treated with tiadenol and clofibrate

the levels of hepatic lipid metabolizing enzymes including palmitoyl-CoA hydrolase, palmitoyl-l-carnitine hydrolase as well as some other enzymes were studied in the 100,000 g × 1 hr sediment, the corresponding supernatant and lipid-rich floating layer from rats fed tiadenol or clofibrate-containing diets (0.3 per cent $\text{w}\text{w}$). Tiadenol administration resulted in a large increase of the total activity of palmitoyl-CoA hydrolase, and of peroxisomal-CoA oxidation, while only a moderate enhancement was obtained after clofibrate feeding. the total activity of palmitoyl-l-carnitine hydrolase was increased more by tiadenol than by clofibrate. the specific activity of the two former enzymes was decreased in the particulate MLP-fraction (100,000 g × 1 hr sediment containing mitochondria, peroxisomes and microsomes) after treatment with tiadenol. The specific activity of palmitoyl-CoA hydrolase was increased more than 10-fold in the cytosolic fraction after administration of tiadenol. Tiadenol increased the specific activity of palmitoyl-l-carnitine hydrolase considerably in the cytosolic fraction, but the activity of this enzyme was little affected by clofibrate treatment. the specific activity of palmitoyl-CoA hydrolase and palmitoyl-l-carnitine hydrolase increased in the lipid-rich floating layer. Since there was also a shift in the distribution of peroxisomal palmitoyl-CoA oxidation and catalase, but not of urate oxidase after treatment with the drugs, it is suggested that the drugs induce peroxisomes with altered membrane characteristics.