Neurokinin B

The group of peptides known as tachykinins include substance P, substance K or neurokinin A, and neuromedin K, ie, neurokinin B, as well as a number of nonmammalian peptides. All members of this family contain the conserved carboxy-terrninal sequence Phe-X-Gly-Leu-Met-NH2, where X is an aromatic, ie, Phe or Tyr, or branched aliphatic, eg, Val or lie, amino acid. In general, this C-terminal sequence is cmcial for tachykinin activity (33) in fact, both the methionineamide and the C-terminal amide are cmcial for activity. The nature of the X residue in this sequence determines pharmacological identity (34,35) thus the substance P group contains an aromatic residue in this position, while the substance K group contains an aliphatic residue (33). 

The neuropeptides are peptides acting as neurotransmitters. Some form families such as the tachykinin family with substance P, neurokinin A and neurokinin B, which consist of 11 or 12 amino acids and possess the common carboxy-terminal sequence Phe-X-Gly-Leu-Met-CONH2. Substance P is a transmitter of primary afferent nociceptive neurones. The opioid peptide family is characterized by the C-terminal sequence Tyr-Gly-Gly-Phe-X. Its numerous members are transmitters in many brain neurones. Neuropeptide Y (NPY), with 36 amino acids, is a transmitter (with noradrenaline and ATP) of postganglionic sympathetic neurones. 

Tachykinin NK3 receptor TK NK3r Neurokinin-3 receptor, neurokinin B receptor, neurokinin-beta receptor, Neuromedin K receptor... 

These are a family of peptides which include substance P, isolated in 1931 but only sequenced in 1971. This peptide has been extensively studied since it was the first major peptide to be extracted from brain but only now are useful antagonists becoming available. Two closely related peptides were then isolated from mammalian tissues and can be added to a number of other tachykinins, many of which are found in amphibians. The name tachykinins originated from the vasoactive effects of substance P but the nomenclature has been resolved into calling the three major mammalian peptides substance P, neurokinin A (NKA) and neurokinin B (NKB) with the corresponding receptors being numbered 1 to 3. The order of potencies at the three receptors as follows ... 

Seizure initiation is likely caused by an imbalance between excitatory (e.g., glutamate, calcium, sodium, substance P, and neurokinin B) neurotransmission and inhibitory (y-aminobutyric acid, adenosine, potassium, neuropeptide Y, opioid peptides, and galanin) neurotransmission. 

Other more recent examples of new receptor subt)rpes include neurokinin, melanocortin and somatostatin receptor subt)q)es. Neurokinins (substance P, neurokinin A and neurokinin B) act at three receptor subtypes NK, NK2 and NK3. Selective ligands are being... 

Other members of this family are neurokinin A and neurokinin B. Substance P is an undecapeptide, while neurokinins A and are decapeptides. 

FIGURE 5—67. Shown here are the amino acid sequences for the three neurokinins substance P, neurokinin A (NK-A) and neurokinin B (NK-B). Substance P has 11 amino acid units and NK-A and NK-B each have 10. Several of the amino acids are the same in these three peptides. 

Neurokinin B and neurokinin B receptors. The third important member of the neurokinin neurotransmitter family is neurokinin B (NK-B). Like NK-A, it is a ten amino acid peptide (decapeptide). Six of the ten amino acids in NK-B are the same as in NK-A, and four of the last five amino acids in the N-terminal tail of NK-B are identical to substance P (Fig. 5-67). 

Neurokinin B is formed from a gene called PPT-B, which is different from that from which substance P and NK-A are derived. However, the process of converting the PPT-B protein into NK-B is analogous to that already described for substance P and NK-A (Fig. 5-73). NK-B prefers its own unique receptors, called NK-3 receptors (Fig. 5-73). Neurokinin B and its NK-3 receptors are also mismatched, and in different anatomical areas from substance P, NK-A, and their NK-1 and NK-2 receptors, respectively. 

Substance P belongs to the tachykinin family of peptides, which share the common carboxyl terminal sequence Phe-X-Gly-Leu-Met. Other members of this family are neurokinin A and neurokinin B. Substance P is an undecapeptide, while neurokinins A and B are decapeptides. They have the following structures ... 

Substance P and the related tachykinins neurokinin A and neurokinin B are mainly found in neurons, particularly unmyelinated sensory somatic and visceral fibres, in enteric sensory neurons and in a number of pathways within the brain. The release of tachykinins from the peripheral ends of these neurons may play an important role in the neurogenic inflammatory responses to local injury and inflammation by promoting the release of histamine from mast cell degranulation, and the release of cytokines from invading white cells, as well as acting directly upon blood vessels to produce vasodilation and plasma extravasation. Neurogenic inflammation within... 

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