TAC1, also known as protachykinin 1, is a member of the tachykinin peptide hormone family. TAC1 are a family of peptides that have similar biologic activities and share a common C-terminal sequence, phe-X-gly-leu-met-NH2, but have distinct N-terminal sequences that convey receptor specificities. TAC1 is thought to function as neurotransmitters which interact with nerve receptors and smooth muscle cells. It is known to induce behavioral responses and function as vasodilators and secretagogues. Recombinant human TAC1 protein, fused to His-tag at N-terminus, was expressed in E.coli.