Molecular Pharmacology, Vol 12, 536-545, Copyright © 1976 by the American Society for Pharmacology and Experimental Therapeutics

Membranes of the Adrenal Medulla: a Comparison between the Membranes of the Golgi Apparatus and Chromaffin Granules

¹ Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada H3G 1Y6

A comparative biochemical study of the membranes of the Golgi apparatus and chromaffin granules is described. Chromaffin granule membranes were almost completely devoid of galactosyltransferase activity, a Golgi marker enzyme, and 5'-nucleotidase activity. High specific activities of these two enzymes were detected in the Golgi-rich fraction, which, in addition, showed a small content of dopamine -hydroxylase, as indicated by electrophoretic, immunological, and chemical techniques. The specific activity of dopamine -hydroxylase was 12 times greater in chromaffin granule membranes than in Golgi membranes. Gel electrophoresis also showed the presence in both types of membranes of a band (component C) of similar mobility. Component C was highly concentrated in Golgi membranes. The molar ratio of cholesterol to phospholipid and the lysolecithin content were greater in the granules than in the Golgi membranes. Greater specific activities of Mg²⁺- and Ca²⁺-dependent ATPases were detected in Golgi membranes. However, transphosphorylation from ATP to membranes was 16 times greater in the granules than in the Golgi membranes. The results are discussed in connection with the origin of chromaffin granules, and it is concluded that, if chromaffin granules are derived from the Golgi apparatus, a specific process of "membrane differentiation" must take place in order to explain the marked biochemical differences between the two types of membranes.

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ACKNOWLEDGMENTS We are grateful to Miss C. Shorten and Mrs. C. Ulpian for their skillful technical assistance. We wish to thank Dr. B. Collier for his helpful comments.