ABSTRACT
This chapter deals with enzymes involved in the synthesis of catecholamines. Tyrosine is converted to epinephrine in a four-step process that is catalysed by tyrosine hydroxylase (TH), aromatic-L-amino-acid decarboxylase, dopamine β-hydroxylase (DβH), and phenylethanolamine N-methyltransferase (PNMT). TH apparently exists within the chromaffin cell in an inactive or active form. The chapter discusses general aspects of the activation, followed by a discussion of specific mechanisms of activation, primarily phosphorylation. TH is in a class of mammalian enzymes in which the catalytic activity is dependent on tetrahydrobiopterin as an electron donor. Aromatic L-amino acid decarboxylase catalyzes the conversion of dopa to dopamine and other reactions. This is a ubiquitous enzyme that is in no way rate-limiting in the synthesis of catecholamines. DβH is a copper-containing enzyme. The enzyme-bound copper is essential for activity and alternates between the cuprous and cupric states during catalysis. PNMT catalyzes the conversion of norepinephrine to epinephrine.
