Molecular Pharmacology, Vol 11, 694-699, Copyright © 1975 by the American Society for Pharmacology and Experimental Therapeutics

Importance of the Aromatic Ring in Adrenergic Amines

Nonaromatic Analogues of Phenylethanolamine as Substrates for Phenylethanolamine N-Methyltransferase

¹ Department of Medicinal Chemistry, School of Pharmacy, University of Kansas, Lawrence, Kansas 66045
² Department of Biochemistry, McCollum Laboratories, University of Kansas, Lawrence, Kansas 66045

Various nonaromatic analogues of phenylethanolamine were evaluated as substrates for phenylethanolamine N-methyltransferase (EC 2.1.1). In general the nonaromatic analogues were as good as, if not better than, phenylethanolamine itself as substrates for this enzyme. Evidence that these compounds were being N-methylated by phenylethanolamine N-methyltransferase was obtained by isolating and identifying the N-methylated products. Competitive experiments using phenylethanolamine also provided evidence that phenylethanolamine N-methyltransferase was the enzyme carrying out this methylation. The results of these studies suggest that the role of the aromatic ring of phenylethanolamine in binding to this enzyme would be due to its hydrophobic character, rather than its electron-rich nature. The data presented here are inconsistent with the possibility of a charge-transfer complex being formed during the binding of phenylethanolamine to phenylethanolamine N-methyltransferase, but instead suggest the existence of a hydrophobic binding site on the enzyme for this portion of the substrate molecule.