Subcellular distribution of ascorbate in bovine adrenal medulla: Evidence for accumulation in chromaffin granules against a concentration gradient

• Published in: Biochimica et biophysica acta Vol. 628; no. 2; pp. 182 - 189
• Main Authors: Ingebretsen, Ole C., Terland, Ole, Flatmark, Torgeir
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.01.1980
• Subjects: Adrenal Cortex; Adrenal Cortex - metabolism; Adrenal Medulla; Adrenal Medulla - metabolism; animal physiology; Animals; Ascorbic Acid; Ascorbic Acid - metabolism; Catecholamines; Catecholamines - metabolism; Cattle; Chromaffin Granules; Chromaffin Granules - metabolism; Chromaffin System; Chromaffin System - metabolism; Dehydroascorbic Acid; Dehydroascorbic Acid - metabolism; metabolism; Subcellular Fractions; Subcellular Fractions - metabolism
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/0304-4165(80)90365-7

The subcellular distribution of ascorbate and catecholamines has been studied in homogenates of bovine adrenal medulla and cortex. 1. 1. The recovery of the vitamin was found to be 4.10 ± 0.22 and 9.57 ± 1.37 μmol/g wet weight for the medulla and cortex, respectively. A major fraction (34.4%) of the vitamin was recovered in the particulate fraction of the medulla as compared to about 8% in the corresponding fraction of the cortex. In comparison, 78.9% of the catecholamines were found in the particulate fraction of the medulla. 2. 2. Analytical differential centrifugation of medulla homogenates revealed a sedimentation profile of ascorbate which was identical to that obtained for noradrenalin and adrenalin. The co-sedimentation of these compounds indicates that ascorbate is an essential component of the heavy as well as the light population of chromaffin granules. The stoichiometry of catecholamines to ascorbate was approx. 25:1 in both subpopulations. 3. 3. Based on an estimated volume fraction of ∼13% for the chromaffin granules, as determined morphometrically (Kryvi, H., Flatmark, T. and Terland, O. (1979) Eur. J. Cell Biol. 20, 76–82), a concentration gradient (chromaffin granules:cytosol) of approx. 4 was estimated for ascorbate in the cells of adrenal medulla. 4. 4. No ascorbate 2-sulfate was detected in any of the subcellular fractions isolated, and the content of dehydroascorbate in isolated chromaffin granules was <1% of the total ascorbate value.