Converts tyrosine into tyramine, a precursor of isoquinoline alkaloids and various amides. H(+) + L-tyrosine = CO2 + tyramine Homotetramer. A number of isoforms are produced. According to EST sequences. Expressed specifically in flowers. Induced by drougt stress, wounding and methyl jasmonate. Slight reduction of pollen grain size. Belongs to the group II decarboxylase family.