Neurokinin A

Neurokinin A (formerly known as substance K) is a member of the tachykinin family of neuropeptide neurotransmitters. It is produced from the same preprotachykinin A gene as the neuropeptide substance P. It has various roles in the body of humans and other animals. One specific example is mediating contraction of the rat colon and bronchoconstriction through the non-adrenergic non-cholinergic nervous system (a branch of the vagal system). Neuropeptide K (which has also been called neurokinin K ) and neuropeptide gamma are N-terminally longer versions of neurokinin A, produced from the same splice forms of the same gene, which appear to be final peptide products in some tissues.

Structure
Structure of mammalian neurokinin A was obtained using CD spectropolarimetry and 2D proton NMR. Analysis showed that in water, the peptide adopts an extended conformation while in the presence of micelles (a model cell membrane system), an alpha helical conformation is induced in the central core (Asp4-Met10).