Disulfides oxytocin

Disulfides. As shown in Figure 4, the and h-chains of insulin are connected by two disulfide bridges and there is an intrachain cycHc disulfide link on the -chain (see Insulin and other antidiabetic drugs). Vasopressin [9034-50-8] and oxytocin [50-56-6] also contain disulfide links (48). Oxidation of thiols to disulfides and reduction of the latter back to thiols are quite common and important in biological systems, eg, cysteine to cystine or reduced Hpoic acid to oxidized Hpoic acid. Many enzymes depend on free SH groups for activation—deactivation reactions. The oxidation—reduction of glutathione (Glu-Cys-Gly) depends on the sulfhydryl group from cysteine. 

Oxytocin is a cyclic compound containing a disulfide bridge between two cysteine residues. 

The three-dimensional structure of oxytocin. The sulfur atoms of the disulfide bridge are in yellow. The ... 

Noszal, B. Guo, W. Rabenstein, D. L., Characterization of the macroscopic and microscopic acid-base chemistry of the native disulfide and reduced dithiol forms of oxytocin, arginine-vasopressin and related peptides, J. Org. Chem. 57,2327-2334 (1992). 

D Sahal. Removal of iodine by solid phase adsorption to charcoal following iodine oxidation of acetamidomethyl-protected peptide precursors to their disulfide bonded products oxytocin and a Pre-S, peptide of hepatitis B illustrate the method. Int J Pept Res 53, 91, 1999. 

By comparing time-resolved and steady-state fluorescence parameters, Ross et alm> have shown that in oxytocin, a lactation and uterine contraction hormone in mammals, the internal disulfide bridge quenches the fluorescence of the single tyrosine by a static mechanism. The quenching complex was attributed to an interaction between one C — tyrosine rotamer and the disulfide bond. Swadesh et al.(()<>> have studied the dithiothreitol quenching of the six tyrosine residues in ribonuclease A. They carefully examined the steady-state criteria that are useful for distinguishing pure static from pure dynamic quenching by consideration of the Smoluchowski equation(70) for the diffusion-controlled bimolecular rate constant k0,... 

In heterodetic peptides, the ring system is formed from amides and other heteroatom linkages, for example, a disulfide bridge, a thioether or a lactone linkage. The most common nonamide links in heterodetic peptides are the disulfide bonds (found in posterior pituitary hormones such as oxytocin and vasopressin) and the ester (lactone) fnnction. " ... 

The iodine oxidation method has also been applied in one-pot synthetic strategies to mono-disulfide peptides in which the bis-cysteine peptide is cleaved from the resin, depro-tected, and oxidized in a single step.163 64 A comparative analysis of the iodine procedure (TFA/10 equiv I2) with other TFA/oxidant mixtures using oxytocin as the target model peptide clearly revealed formation of side products to a significant extent. 85 ... 

The deamino-dicarba-analogues of various biologically active cystine-containing peptides, such as oxytocin/1-3 calcitonin/31 32 and somatostatin/33-35 have shown high biological activity and enhanced metabolic and chemical stability owing to the absence of reducible disulfide linkages. 

Oxytocin (OT) is a nonapeptide in which six amino acids form a ring closed by a disulfide bridge, while the ring itself forms an antiparallel pleated sheet. The tail portion of the peptide, composed of Pro-Leu-Gly-NHj, is also rigidly held in a folded conformation. Oxytocin causes the powerful contraction of some smooth muscles and plays a vital role in milk ejection (not to be confused with milk secretion, which is regulated by prolactin). It also has uterotonic action, contracting the muscles of the uterus, and is therefore used clinically to induce childbirth. 

Oxytocin is a 9-amino-acid peptide with an intrapeptide disulfide cross-link (Figure 37-5). Its amino acid sequence differs from that of vasopressin at positions 3 and 8. 

Oxytocin is a nine-amino-acid peptide composed of a six-amino-acid disulfide ring and a three-membered tail (Figure 37-2). Oxytocin and vasopressin differ from vasotocin—the only posterior... 

Another type of covalent bond in proteins is the disulfide bond, formed by oxidative coupling of the -SH groups in cysteine. Oxytocin is an example of a cyclic peptide with a S-S bond. 

The posterior pituitary gland is the source of circulating oxytocin and vasopressin (iantidiuretic hormone, ADH). These hormones are actually produced in specific nerve cells in the hypothalamus and travel down the axons into the neuro-hypophysis. The structures of oxytocin and vasopressin are shown in Chapter 4. It may be seen that both are nanopeptides with disulfide bonds and that they differ by two amino acids only. Both hormones originate from larger proteins vasopressin from prepressophysin and oxytocin from pro-oxyphysin. These are converted to pressophysin and oxyphysin, respectively (collectively,... 

Two cysteine residues may form a disulfide bridge within a single peptide chain, making a ring. Figure 24-9 shows the structure of human oxytocin, a peptide hormone that causes contraction of uterine smooth muscle and induces labor. Oxytocin is a nonapeptide with two cysteine residues (at positions 1 and 6) linking part of the molecule... 

Structure of human oxytocin. A disulfide linkage holds part of the molecule in a large ring. 

Figure 24-14 shows the first two steps in the sequencing of oxytocin. Before sequencing, the oxytocin sample is treated with peroxyformic acid to convert the disulfide bridge to cysteic acid residues. 

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