PT - JOURNAL ARTICLE AU - ROBERT G. PENDLETOX AU - INA B. Snow TI - The Binding Order of Substrates to Phenylethanolamine <em>N</em>-Methyltransferase DP - 1973 Nov 01 TA - Molecular Pharmacology PG - 718--725 VI - 9 IP - 6 4099 - http://molpharm.aspetjournals.org/content/9/6/718.short 4100 - http://molpharm.aspetjournals.org/content/9/6/718.full SO - Mol Pharmacol1973 Nov 01; 9 AB - We have studied the substrate binding order of S-adenosylmethionine and norepinephrine to phenylethanolamine N-methyltransferase via the use of two inhibitors of this enzyme. 2-(2,5-Dichlorophenyl)cyclopropylamine hydrochloride (SK&amp;F 9208) competitively inhibited norepinephrine as the variable substrate but was an uncompetitive inhibitor with respect to S-adenosylmethionine. S-Adenosylhomocysteine, however, was a competitive inhibitor with respect to S-adenosylmethionine but noncompetitive as an antagonist of norepinephrine. These studies are interpreted to suggest a kinetically ordered pattern of substrate binding to the enzyme, with S-adenosylmethionine being initially bound. ACKNOWLEDGMENTS The authors wish to thank Mr. George Gessner, Miss Deborah Seltz, and Miss Julie Wang for their excellent technical assistance in carrying out this project. A special note of thanks is also due Dr. Harry Green for his helpful encouragement of our efforts.