Catalyzes the decarboxylation of L-tryptophan to tryptamine and L-5-hydroxytryptophan to serotonin, respectively. H(+) + L-tryptophan = CO2 + tryptamine 5-hydroxy-L-tryptophan + H(+) = CO2 + serotonin Homodimer. Belongs to the group II decarboxylase family.