Esterification of free fatty acids by subcellular preparations of rat adipose tissue

The intracellular location of the enzymes responsible for catalyzing the esterification of [14C]palmitate with α-glycerophosphate was studied with enzyme fractions prepared by centrifugation of adipose tissue homogenates, Esterifying activity was confined to mitochondrial and microsomal fractions, the mitochondria being the more active. ATP and CoA were obligatory requirements. 2. With either particulate fraction, phospholipids were the principal ester products ; phosphatidic acid was tentatively identified as being the major phospholipid formed. 3. The soluble fraction (109000 × g supernatant fluid) when used alone did not stimulate esterification. However, addition of this fraction to particulate preparations, produced a consistent alteration in ester products so that tri- and diglyceride became the major products, while net formation of ester bonds was only modestly increased. 4. The soluble fraction was found to exert its effect after binding of free fatty acids to subcellular particles. The factor(s) responsible for the activity of the soluble fraction could also be bound by these particles. The soluble fraction activity persisted after heating to 58° and was slowly dialyzable. Its effect could not be replicated by a variety of proteins and ions. 5. It is suggested that the effect of the soluble fraction was due to stimulation of particulate phosphatidate phosphohydrolase activity.