Pathway of noradrenaline formation from DOPA.

Three compounds have each been postulated as the possible immediate precursor of noradrenaline (1) : p-hydroxyphenylethanolamine, dihydroxyphenylserine, and hydroxytyramine. Erspamer (2) found p-hydroxyphenylethanolamine in the salivary gland of the octopus; however, the compound has not been reported to be present in mammalian tissues, nor has it been shown that it can be converted to noradrenaline by enzymatic action. Beyer (3) and Blaschko et al. (1) have demonstrated that dihydroxyphenylserine is slowly decarboxylated by rabbit and guinea pig kidney extracts to form noradrenaline. Schmiterlow (4) found that the noradrenaline content of rabbit urine was increased after injection of dihydroxyphenylserine. This compound, however, has not been shown to occur in mammalian tissue. Goodall and Kirshner (5) demonstrated that adrenal slices and homogenates could form adrenaline and noradrenaline from tyrosine, from dihydroxyphenylalanine, and from hydroxytyramine, and presented evidence that, in the formation of noradrenaline, tyrosine was successively converted to dihydroxyphenylalanine, hydroxytyramine, and noradrenaline. It is now shown that the alternate pathway, tyrosine to dihydroxyphenylalanine to dihydroxyphenylserine to noradrenaline (Fig. I), is involved, if at all, to only a minor extent in the formation of noradrenaline.