Disulfide links

There are several levels of pepfide sfrucfure The primary structure is the ammo acid sequence plus any disulfide links With the 20 ammo acids of Table 27 1 as building blocks 20 dipeptides 20 tripeptides 20" tetrapeptides and so on are possible Given a peptide of unknown structure how do we determine its ammo acid sequence" ... 

Two protein hormones, inhibin and activin, have been identified in gonadal tissue. Inhibin has been isolated from ovarian foUicular fluid and found to inhibit pituitary secretion of FSH. Inhibin is a glyocoprotein heterodimer consisting of two disulfide-linked subunits, a and P two types of P-subunit,... 

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. 

Fig. 9. A de novo designed P sheet protein, betabellin, formed by the dimerization of two identical four-stranded -sheets and a disulfide linking the two sheets. This model is for betabeUins 9 and later progenies the earher betabeUins contained a two-armed cross-linker connecting the sheets (51).

Calcitonins from several species have been characteri2ed and synthesi2ed. They are all single-chain 32-residue polypeptides (ca 3600 mol wt), although a disulfide link between the first and seventh cysteine residues results in a cycHc stmcture that is indispensable for activity (Eig. 6). 

Describe the stereochemical aspects of the structure of cystine, the structure that is a disulfide-linked pair of cysteines. 

Takae S, Miyata K, Oba M, Ishii T, Nishiyama N, Itaka K, Yamasaki Y, Koyama H, Kataoka K (2008) PEG-detachable polyplex micelles based on disulfide-linked block catiomers as bioresponsive nonviral gene vectors. J Am Chem Soc 130 6001-6009... 

A tridentate SNO ligand coordinates with a bipyridine to give ((2,2 -bipyridine)[2-(2-mercapto-phenyl)iminophenoxy])zinc. The monomeric complex has a distorted trigonal bipyramidal geometry with a phenolate and a thiolate coordinated. The synthesis was carried out electrochemically from anodic zinc in the presence of a disulfide-linked ligand precursor.867... 

Fig. 5. Backscattered Raman and ROA spectra of native (top pair) and reduced (second pair) hen lysozyme, and of native (third pair) and reduced (bottom pair) bovine ri-bonuclease A, together with MOLSCRIPT diagrams of the crystal structures (PDB codes llse and lrbx) showing the native disulfide links. The native proteins were in acetate buffer at pH 5.4 and the reduced proteins in citrate buffer at pH 2.4. The spectra were recorded at 20°C. 

Figure 1.73 The disulfide group of a cystamine-modified protein may undergo disulfide interchange reactions with another sulfhydryl-containing protein to yield a disulfide-linked conjugate.

Figure 21.6 SPDP can be used to activate an antibody molecule through its available amine groups to form a sulfhydryl-reactive derivative. Toxin molecules containing disulfide-linked A-B chains may be reduced with DTT to isolate the A-chain component containing a free thiol. The SPDP-activated antibody is then mixed with the reduced A chain to effect the final conjugate by disulfide bond formation.

Ermacora, M.R., Delfino, J.M., Cuenoud, B., Schepartz, A., and Fox, R.O. (1992) Conformation-dependent cleavage of Staphylococcal nuclease with a disulfide-linked iron chelate. PNAS 89, 6383. 

The antileukemic efficacy of an immunotoxin composed of a monoclonal anti-Thy-1 antibody disulfide linked to the ribosome-inactivating protein gelonin. Cancer Immunol. Immunother. 25, 31. 

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