Acyl-CoA synthetase in rat liver peroxisomes. Computer-assisted analysis of cell fractionation experiments.

Abstract

The subcellular distribution of the acyl coenzyme A synthetases of rat liver was reinvestigated in order to determine whether part of this activity occurs in peroxisomes. Rat liver was fractionated by differential centrifugation and by equilibrium density centrifugation. Acyl-CoA synthetase was assayed using a new, simple extraction procedure on three substrates: palmitate, laurate, and octanoate. Comparison of the resulting synthetase distributions with the distributions of marker enzymes for peroxisomes, mitochondria, and endoplasmic reticulum demonstrated the presence of some synthetase activity in each of the three organelles. These trimodal synthetase distributions were evaluated quantitatively by means of a computer program that calculated optimal linear combinations of marker enzymes using a least squares criterion. Peroxisomes were found to contain 7% of the liver's palmitoyl-CoA synthetase activity and 6% of its lauroyl-CoA synthetase activity, but no demonstrable octanoyl-CoA synthetase activity. The remainder of these activities are divided between the mitochondria and endoplasmic reticulum, in a manner that agrees with previous studies. The chain length specificity of the synthetase(s) of each organelle appears to be unique. The absolute activity of the peroxisomal palmitoyl-CoA synthetase is sufficient to maintain maximal peroxisomal beta-oxidation. Clofibrate treatment of the rats caused a 2.6- to 3.1-fold increase in the liver's total acyl-CoA synthetase activities. The subcellular distribution was not greatly affected by this drug treatment.