Previous biochemical evidence for the localization of phenylethanolamine-N-methyltransferase in adrenal medulla has indicated that this enzyme is soluble, although some workers have reported a significant amount of particulate phenylethanolamine-N-methyltransferase (Joh and Goldstein, 1973). Electron microscopic immunocytochemical study of bovine adrenal medulla has revealed a distinct particulate localization of phenylethanolamine-N-methyltransferase in association with chromaffin granules. It is therefore suggested that some, and possibly most, adrenal phenylethanolamine-N-methyltransferase may be in a particulate form in intact tissue, and that solubilization artifacts during tissue preparation could account in part for the large proportion of soluble phenylethanolarmine-N-methyltransferase reported previously.
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Localization of PNMT at the light microscopic level was demonstrated by Fuxe, Goldstein, HGkfelt and Joh (1971); Goldstein, Fuxe, HGkfelt and Joh (1971); Hijkfelt, Fuxe, and Goldstein u973) with the use of a fluorescent antibody technique. These studies showed that only a portion of adrenal medullary cells contained PNMT, while all medullary cells contained the biosynthetic enzymes for formation of norepinephrine from tyrosine hydroxylase, DOPA decar-- * Supported in part by USPHS Grants GM12,675 and HD06380 (Iowa Toxicology Center). 7 A preliminary report of this research was presented at the NIH Symposium “SIF Cells. Structure and function of the small, intensely fluorescent sympathetic cells,” February 1975. $ Trainees supported by USPHS Grant GMW141.