Subcellular Site of Biosynthesis of the Catecholamine Biosynthetic Enzymes in Bovine Adrenal Medulla

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Abstract
The subcellular site of biosynthesis of the catecholamine biosynthetic enzymes was examined. Free and membrane-bound polysomes were prepared from bovine adrenal medulla and mRNA was isolated from these polysomes. Both were active in directing cell-free translations. Immunoprecipitation of cell-free products with specific antisera localized the biosynthesis of the subunits of tyrosine hydroxylase (TH) (apparent MW = 61,000) and of phenylethanolamine N-methyltransferase (PNMT) (apparent MW = 32,000) on free polysomes, compared with biosynthesis of subunits of dopamine .beta.-hydroxylase (DBH) (apparent MW = 67,000) on membrane-bound polysomes. Cross-reactivity between translation products was observed. Antibodies for DBH recognized a polypeptide with electrophoretic mobility identical to newly synthesized PNMT. Increasing concentrations of antibodies to DBH recognized at most 1/20 of the PNMT formed. The subcellular distribution of the catecholamine synthesizing enzymes is determined by their site of biosynthesis.