Disulfides amino

Sulfhydryl group A disulfide Amino group Quaternary amine... 

The constant potential amperometric detector determines the current generated by the oxidation or reduction of electoactive species at a constant potential in an electrochemical cell. Reactions occur at an electrode surface and proceed by electron transfer to or from the electrode surface. The majority of electroactive compounds exhibit some degree of aromaticity or conjugation with most practical applications involving oxidation reactions. Electronic resonance in aromatic compounds functions to stabilize free radical intermediate products of anodic oxidations, and as a consequence, the activation barrier for electrochemical reaction is lowered significantly. Typical applications are the detection of phenols (e.g. antioxidants, opiates, catechols, estrogens, quinones) aromatic amines (e.g. aminophenols, neuroactive alkaloids [quinine, cocaine, morphine], neurotransmitters [epinephrine, acetylcoline]), thiols and disulfides, amino acids and peptides, nitroaromatics and pharmaceutical compounds [170,171]. Detection limits are usually in the nanomolar to micromolar range or 0.25 to 25 ng / ml. 

The following compounds are used as inhibitors in acid solutions amines, amino-imidazolines, amino- and nitrophenols, aminotriazole, aldehydes, bezothiazol, dibenzyl sulfoxide, dithiophos-phoric acids, guanidine derivatives, ureas, phosphonium salts, sulfonium salts, sulfonic acids, thio-ethers, thioureas, and thiocarbanoyl disulfides. Amino alcohols, aminobenzimidazole, benzoates, quinoline derivatives, cinnamates, fatty amines, polyether amines, silicates, and triazoles are used as inhibitors in neutral or weakly alkaline solutions, while for strongly alkaline solutions, aldehydes and fatty amines are used. 

Hydrogen bonding stabilizes some protein molecules in helical forms, and disulfide cross-links stabilize some protein molecules in globular forms. We shall consider helical structures in Sec. 1.11 and shall learn more about ellipsoidal globular proteins in the chapters concerned with the solution properties of polymers, especially Chap. 9. Both secondary and tertiary levels of structure are also influenced by the distribution of polar and nonpolar amino acid molecules relative to the aqueous environment of the protein molecules. Nonpolar amino acids are designated in Table 1.3. 

GS = choriosomatomammotropin = same amino acid as GH-N. Disulfide bonds cormect Cys molecules at positions 53—165 and 182—189. Asn-140 of... 

The amino acid sequences of hCS-A, hCS-B, and hCS-V are shown in relation to GH in Figure 1. The sequence of hCS-V is predicted from the DNA coding sequence and apparentiy does not possess amino acids 8—55 relative to GH and the other hCS molecules. It is not certain whether hCS-V is expressed or what function it may have. Human CS-A and hCS-B share approximately 85% identity with GH and also possess the disulfide bonds between Cys 53—165 and Cys 182—189 which produce the long and short S—loops characteristic of the PRL/GH family. 

Human growth hormone is a single polypeptide chain of 191 amino acids (qv) having two disulfide bonds, one between Cys-53 and Cys-165, forming a large loop in the molecule, and the other between Cys-182 and Cys-189, forming a small loop near the C-terminus. The stmcture of hGH is shown in Figure 1 molecular mass is 22,125 the empirical formula is C qH 29N 262 300 7 ... 

Fig. 1. Primary stmcture of hGH showing the amino acid sequence and the disulfide bonds.

Synthesis from Thiohydantoins. A modification (71) of the Bucherer-Bergs reaction consisting of treatment of an aldehyde or ketone with carbon disulfide, ammonium chloride, and sodium cyanide affords 2,4-dithiohydantoias (19). 4-Thiohydantoias (20) are available from reaction of amino nitriles with carbon disulfide (72). Compounds (19) and (20) can be transformed iato hydantoias. 

Fig. 1. Amino acid sequence for the A- and B-chains of human iasulin [11061-68-0] where soHd lines denote disulfide bonds. Porciae iasulin [12584-58-6] differs by one amino acid ia the B-chaia where alanine replaces threonine at positioa 30. Boviae iasulia [11070-73-8] differs by three amino acids. la the A-chain alanine replaces the threonine at positioa 8 and valine replaces the isoleuciae at position 10. In the B-chain there is an alanine at position 30.

Amino-4,6-dichlorophenol. This compound (11) forms long white needles from carbon disulfide, and aggregate spheres from benzene. It sublimes at 70—80°C (8 Pa = 0.06 mm Hg) and decomposes above 109 °C. It is freely soluble in benzene and carbon disulfide, and is sparingly soluble in petroleum ether, water, and ethanol. The free base is unstable and the hydrochloride salt (mp 280—285°C, dec) is employed commercially. 

The solubility in alkali sulfide solutions stems from the presence of disulfide groups —S—S— in ortho position to the terminal amino groups. These disulfide groups are reduced to the mercapto groups —SH, which are soluble in alkaU. 

Thaumatin. Thaumatin [53850-34-3] is a mixture of proteins extracted from the fmit of a West African plant, Thaumatococcus daniellii (Beimett) Benth. Work at Unilever showed that the aqueous extract contains two principal proteins thaumatin I and thaumatin II. Thaumatin I, mol wt 22,209, contains 207 amino acids in a single chain that is cross-linked with eight disulfide bridges. Thaumatin II has the same number of amino acids, but there are five sequence differences. Production of thaumatins via genetic engineering technology has been reported (99). 

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