Abstract
The activities of histamine methyltransferase preparations partially purified from several mammalian sources are activated by low concentrations of histamine (Km = 6-9 µM) and are markedly inhibited by histamine concentrations in excess of 10 µM. A variety of antihistaminic drugs are potent competitive inhibitors of histamine methyltransferase in the presence of histamine concentrations below 10 µM, but enhance enzyme activity at higher histamine concentrations. These effects of antihistamines correlate partially with their antihistaminic activity.
ACKNOWLEDGMENTS We wish to thank the following companies for donations of drugs: d-chlorpheniramine maleate. d-brompheniramine maleate, l-chlorpheniramine maleate, l-brompheniramine maleate, and chlorpheniramine maleate, Schering Corporation; brompheniramine maleate, A. H. Robins Company; chlorcyclizine hydrochloride and triprolidine hydrochloride, Burroughs Wellcome and Company; bromdiphenhydramine hydrochloride and diphenhydramine hydrochloride, Parke, Davis and Company; diphenylpyramine hydrochloride and chlorpromazine hydrochloride. Smith Kline & French Laboratories, carbinoxamine maleate and haloperidol, McNeil Laboratories; dimethindene, antazoline phosphate, and tripelennamine hydrochloride, Ciba Pharmaceutical Company; fenazoxine hydrochloride and orphenadrine hydrochloride, Riker Laboratories; promethazine hydrochloride, Wyeth Laboratories; pyrathiazine hydrochloride, Upjohn Company; thioridazine, Sandoz Pharmaceutical Company; cyclizine, Sterling-Winthrop Research Institute; chlordiazepoxide and diazepam, Hoffmann-La Roche, Inc.; pentobarbital sodium, Abbott Laboratories; and α-hydrazinohistidine, Merck Institute for Therapeutic Research. We would like to thank Drs. Donald Coffey, Allen Fenselau, and David Chou for their advice on some of the theoretical aspects of this work, and Mrs. Birgitta Brown for her technical assistance.
- Copyright ©, 1972, by Academic Press, Inc.
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