– Protachykinin-1(TAC1) is a secreted protein and belongs to the tachykinin family. TAC1 is encoded by the TAC1 gene. This gene encodes four products of the tachykinin peptide hormone family, substance P and neurokinin A, as well as the related peptides, neuropeptide K and neuropeptide gamma. These hormones are thought to function as neurotransmitters which interact with nerve receptors and smooth muscle cells. They are known to induce behavioral responses and function as vasodilators and secretagogues.