Figure 3.

Tyrosine is metabolised by a hydroxylase in dihydroxyphenylalanine (DOPA) that in turn is decarboxylated in dopamine. Dopamine can be hydroxylated in noradrenaline that in turn can be methylated by Phenylethanolamine N-Methyltransferase (PNMT) to form adrenaline. Dopamine, noradrenaline and adrenaline are inactivated by methylation forming metanephrines that can be sulphated or further metabolised by monoamine oxidases in homovanillic and vanillylmandelic acids (HVA and VMA, respectively).