converts norepinephrine into epinephrine. Thus, a cell that uses epinephrine as its transmitter contains four enzymes (TH, AADC, DBH, and PNMT), whereas norepinephrine neurons contain only three enzymes (lacking PNMT) and dopamine cells only two (TH and AADC).

Degradation

Catecholamines have a half-life of a few minutes when circulating in the blood. They can be degraded either by methylation by catechol-''O''-methyltransferases (COMT) or by deamination by monoamine oxidases (MAO).

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