2 DISTINCT LONG-CHAIN-ACYL COA SYNTHETASES IN GUINEA-PIG HARDERIAN-GLAND

Two distinct long-chain-acyl-CoA synthetases which have different kine tic properties were identified in the guinea pig Harderian gland. One was localized in the microsomes and the other in the mitochondria. The relative V-max values of die microsomal enzyme were 8.1, 1.7 and 1 an d the apparent K-m values were 66.7. 12.0 and 30.0 mu M for palmitic, linoleic and arachidonic acids, respectively. The relative V-max value s of the mitochondrial enzyme were 2.7, 3.5 and 1 and the apparent K-m values were 33.3, 29.9 and 30.0 mu M for palmitic, linoleic and arach idonic acids, respectively. The relative V-max values for the liver mi crosomal enzyme were 2.0, 2.5 and 1, while those of the liver mitochon drial enzyme were 4.1, 3.9 and 1 with palmitic, linoleic and arachidon ic acids, respectively. There were no difference between the microsoma l and the mitochondrial enzymes in the liver, regarding apparent K-m v alues; these were 38.4, 29.9 and 22.0 mu M for palmitic, linoleic and arachidonic acids, respectively, Thus, the substrate specificity and c atalytic rate of the mitochondrial enzyme in Harderian gland for palmi tic. linoleic and arachidonic acids were similar to the liver enzyme, but not to the microsomal enzyme in Harderian gland. On the other hand , the antiserum raised against the rat liver enzyme immune-titrated an d immune-blotted the enzymes from Harderian gland microsomes and liver , but not so the enzyme from Harderian gland mitochondria. Thus, the m icrosomal enzyme in Harderian gland had a common immunogenic epitope(s ) with the liver enzyme, but the mitochondrial enzyme did not. The Har derian gland mitochondrial enzyme was a distinct protein from liver en zymes. The catalytic and immunogenic characteristics suggest that the enzyme proteins in the Harderian gland are unique, that is, different from that in the liver. The large V-max value of the Harderian gland m icrosomal enzyme for palmitic acid suggests that it contributes to the synthesis of a large amount of the secretory lipid and the high K-m v alue to maintenance of cellular lipid in this organ. The evidence that long-chain-acyl-CoA synthetase in the mitochrondria is distinct from that in the microsomes was first found in guinea pig Harderian gland.