Formation of Histamine: Histidine Decarboxylase

Histidine decarboxylase (HDC, L -histidine carboxylyase, EC 4.1.1.22) catalyses the decarboxylation of L -histidine to histamine. It is the only enzyme that forms histamine (Schayer 1966, 1978). There have been a great number of papers on histamine (including more than ten monographs), but it is only recently that studies on HDC have been carried out at the molecular level (Watanabe and Wada 1983). The enzyme is very labile and the tissue content is extremely low, and it has therefore been difficult to purify (Aures et al. 1970; Aures and HAkanson 1971). Most interest in HDC has centered on: (a) its inhibitors, which deplete tissues of histamine (Beaven 1982; Kollonitsch 1982) and may be useful clinically or in pharmacological research; and (b) its antibody, which may serve as a probe in the immunohistochemical identification of the histaminergic neurone system in the CNS (Watanabe et al. 1983, 1984; Pollard and Schwartz 1986), since histamine itself, unlike other monoamines, does not give strong, specific fluorescence suitable for its histochemical identification.