Precursor of a mitochondrial enzyme accumulates in the cytoplasm of preen glands for a specialized function

Malonyl-CoA decarboxylase in the mitochondria of the liver of goose is immunologically identical with the decarboxylase in the cytoplasm of the uropygial gland (Buckner et al. (1978) $\text{Arch. Biochem. Biophys.}$ 186, 152–163). Messenger RNA was isolated from the liver and the uropygial gland and translated in a rabbit reticulocyte system. Specific immunoprecipitation of the translation products with anti malonyl-CoA decarboxylase showed that in both cases the primary translation product was a 50 K dalton peptide identical in size to the cytoplasmic enzyme in the gland. Specific immunoprecipitation of malonyl-CoA decarboxylase from liver slices which had been incubated with ³⁵S]methionine showed that the mature mitochondrial enzyme was a 47 K dalton peptide, 3 K daltons smaller than the primary translation product and the isolated cytoplasmic enzyme. These results suggest that the decarboxylase is proteolytically processed during transport into the mitochondria and that the large amount of the cytoplasmic decarboxylase found in the gland represents accumulation of the unprocessed precursor form of the normally mitochondrial enzyme.