Peptides reptiles

Oxytocin, a nine amino acid peptide, is synthesized primarily in the paraventricular and supraoptic (SON) nuclei of the hypothalamus, from which it is released to the general circulation through the posterior pituitary (Insel et ah, 1997). However, oxytocinergic fibers have also been found to project from the PVN to the limbic system and several autonomic centers in the brain stem. This central OT pool appears to be independent of pituitary OT release cerebrospinal fluid (CSF) and plasma OT responses to numerous stimuli are not correlated (Insel, 1997). Oxytocin and its analog (or partner) peptide vasopressin are found only in mammals. A related peptide, vasotocin, thought to be the evolutionary precedent of these peptides, is found in reptiles and birds. The first known actions of OT were its peripheral effects on the physiology of new mothers. In mammals, OT stimulates milk ejection and uterine contraction, essential aspects of maternal physiology (Insel et ah, 1997). 

Tachykinin family, one of the largest peptide families occurring in nature. The sequence of tachykinins from mammals, birds and reptiles are quite similar, whereas tachykinin peptides from amphibians and fish are fairly diverse. The mammalian tachykinins comprise substance P (SP), the neurokinins A (NKA) and B (NKB), and two elongated versions of NKA, neuropeptide y (NPy) and neuropeptide K (NPK), the endokinins A-D, and hemokinin-1. Members of the non-mammalian tachykinins are, for example, bufokinin, eledoisin, physalaemin, -> kassinin, and up-erolein. A characteristic feature of the tachykinins is the conserved C-terminal pentapeptide amide motif tachykinins). The amino termini of the tachykinins are quite variable, but classes of vertebrate tachykinins with stmctural similarities... 

In humans, perhaps the best-known example of an aggregated P-sheet containing fibrous protein is P-keratin, an aggregated P-sheet-containing protein. P-Keratin is the major constituent of human nail, bird feather calamus and rachis, and reptile scales and claws. This differs from amyloids by having a P-structure in which the peptide chains are parallel, rather than perpendicular, to the direction of the fibril axis. 

Prompted by curiosity, Katsoyannis and du Vigneaud synthetized [80] in 1958, a peptide with the ring of oxytocin and the side chain of vasopressin. The hybrid molecule, vasotocin, had the biological properties of both parent hormones. Soon after its synthesis the peptide was detected in extracts from the pituitary glands of birds and reptiles and later in the pineal gland of mammals, including man. 

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