Decarboxylation to tyramine is not a major route of tyrosine metabolism in mammals.

We have examined the question of the contribution of decarboxylation of tyrosine to tyramine to the overall metabolic fate of tyrosine in mammalian organisms. Since this enzymatic step is independent of oxygen while the loss of the carboxyl group via the transaminase-hydroxylase major pathway is oxygen dependent, we studied the rate of ¹⁴CO₂ release from tyrosine in the presence and absence of oxygen. These studies indicate that a trivial amount of tyrosine is processed by direct decarboxylation to tyramine, even at high substrate levels. Tyrosine metabolism precedes via the well-established pathway which is launched by transamination.