SYNTHESIS, SUBCELLULAR DISTRIBUTION AND TURNOVER OF DOPAMINE β‐HYDROXYLASE IN ORGAN CULTURES OF SYMPATHETIC GANGLIA AND ADRENAL MEDULLAE

— The synthesis, subcellular distribution and turnover of dopamine β‐hydroxylase was studied in organ cultures of rat adrenal medullae and superior cervical ganglia. After exposure to [ 3 H]leucine for 1 or 3 h, the tissues were homogenized at various time intervals and the amount of labelled dopamine β‐hydroxylase in different subcellular fractions (cytosol, soluble and membrane‐bound fraction of catecholamine storage vesicles) was determined by immunoprecipitation and subsequent electrophoresis. In cultured adrenal medullae, induction of dopamine β‐hydroxylase initiated in vivo by administration of reserpine affected both soluble and membrane‐bound pools of dopamine β‐hydroxylase to a similar extent after pulse‐labelling for 1 or 3 h. The half‐lives of dopamine β‐hydroxylase, which amounted to 6 h for the cytosol, 7.5 h for the soluble vesicular and 32 h for the membrane‐bound vesicular pools were not altered by pretreatment with reserpine. In superior cervical ganglia the half‐lives of the soluble pools were 2–3 times longer than in the adrenal medulla, whereas the half‐life of the membrane‐bound fraction was the same as in the adrenal medulla. In both organs the most heavily labelled fraction (both after a pulse of 1 or 3 h) was always that of the vesicular membrane, suggesting that newly‐synthesized dopamine β‐hydroxylase is immediately incorporated into the storage vesicles and not via release into the cytosol from the site of synthesis. The fact that the half‐life of membrane‐bound dopamine β‐hydroxylase is markedly longer than that of the two soluble pools suggests that the single pools are not only independently supplied by newly‐synthesized DBH but there is also no appreciable subsequent exchange between soluble and membrane‐bound pools.