Phenylalanine is an essential amino acid which can be oxidised at position
4 of the aromatic ring by phenylalanine hydroxylase (PAH) to
form tyrosine. PAH (also known as phenylalanine 4-mono-oxygenase),
needs tetrahydrobiopterin (BH4) as a co-factor. Tyrosine is a precursor
of the catecholamine hormones: dopamine, noradrenaline and
adrenaline; and also the thyroid hormone thyroxine. Adrenaline (the
English name from the Latin roots which describes its anatomical relationship
to the “kidney”) has been named in their spirit of independence
by our American cousins as epinephrine from the Greek roots meaning
“above the kidney”. The name derives from its secretion by the medulla
of the adrenal gland (which is situated above the kidney) and awaits
renaming by the New World as the “epinephral” gland!