Edited by Holger Stark Chapter 3 Histamine Metabolism H.G. Schwelberger1, F. Ahrens2, W.A. Fogel3, F. Sánchez-Jiménez4 1Molecular Biology Laboratory, Department of Visceral, Transplantation and Thoracic Surgery, Medical University Innsbruck, Austria, e-mail:
[email protected] 2Department of Veterinary Science, Institute of Animal Physiology, Ludwig-Maximilians University Munich, Germany 3Department of Hormone Biochemistry, Medical University of Lodz, Poland 4Department of Molecular Biology and Biochemistry, University of Malaga, Spain Abstract Histamine is formed by decarboxylation of the amino acid L-histidine, a process catalyzed by histidine decarboxylase (HDC) and can be inactivated either by methylation of the imidazole ring, catalyzed by histamine N-methyltransferase (HMT) or by oxidative deamination of the primary amino group, catalyzed by diamine oxidase (DAO). This chapter describes the enzymatic reactions and the properties of the enzymes involved, including their structures, their cellular localization, their genes, expression and regulation, and the determination of their enzymatic activities. It also addresses cellular histamine transport, storage and release. Further, it discusses alterations in histamine metabolism associated with human diseases and how this might affect histamine receptor signaling. 3.1. Introduction Histamine [2-(1H-Imidazol-4-yl)ethanamine] is an important mediator of many biological processes including inflammation, gastric acid secretion, neuromodulation, and regulation of immune function