Cysteine, III

SG, glutathionyl I, A-acet l-S-(2-liydroxypropyl)-L-cysteine II, 7V-acetyl-S-(2-oxopropyl)-L-cysteine III, A -acet l-S-( 1 -carboxyetliy l)-L-cysteiiie From Bartels and Timchalk (1990)... 

Other sulfur compounds. Several dithiocarbamates con-taining disulfide functions were non-protective in mice, as well as the S-benzyl dithiocarbamate of ethylenediamine. The S-trlthiocarbonate N-dithlocarbajnate of cysteine. III, however,... 

Moggach, S.A., Allan, D.R., Clark, S.J., Gutmann, M.J., Parsons, S., Pulham, C.R., Sawyer, L. High-pressure polymorphism in L-cysteine the crystal structures of L-cysteine-III and L-cysteine-FV, Acta Crystallogr. B62 (2006) 296-309. 

All the complexes consist of several subunits (Table 2) complex I has a flavin mononucleotide (FMN) prosthetic group and complex II a flavin adenine dinucleotide (FAD) prosthetic group. Complexes I, II, and III contain iron-sulphur (FeS) centers. These centers contain either two, three, or four Fe atoms linked to the sulphydryl groups of peptide cysteine residues and they also contain acid-labile sulphur atoms. Each center can accept or donate reversibly a single electron. 

Only the ligands of the Rieske cluster, the two cysteines forming the disulfide bridge, and one glycine are fully conserved in all Rieske proteins (see Section III,A,1)... 

The structure of phthalate dioxygenase reductase that transfers electrons directly from NADPH to phthalate dioxygenase has been determined by X-ray crystallography (119). In class II or class III dioxygenases, the ferredoxin obligately transfers electrons from the reductase to the terminal dioxygenase (64a) it can be either a Rieske-type ferredoxin or a ferredoxin containing a 4-cysteine coordinated [2Fe-2S] cluster. 

In reduced Fe2S2 there is a localization of valences between Fe(III) and Fe(II). The for both ions is shorter than that of the Fe(II) monomer (Table I), whereas the linewidths of the signals of the Fe(III) and Fe(II) domains depend on coefficients obtainable from the solution of Eq. (4). As a result, the signals of the H/3 protons of the cysteines bound to the Fe(III) are shifted beyond 100 ppm downfield with relatively large linewidths, while those of the cysteines bound to the Fe(II) domain are closer to the diamagnetic region and 5-10 times narrower (50-53) (Fig. 2B). There are cases in which there is delocalization of the valences (54, 55) but no NMR investigation is available. 

Like the other paralytic toxins from Conus venom, a-conotoxins are small and very tightly folded, structural features which may be advantageous for rapid paralysis of prey (1). a-Conotoxins are typically 13 to 15 amino acids long with two disulfide bridges (see Table III). In addition to the five a-conotoxins shown, two new a-conotoxins (SIA and SIB) from C. striatus have recently been isolated, sequenced, and chemically synthesized. SIA is very unusual because it is 19 amino acid residues long and it contains 6 cysteine residues, three of which are contiguous near the amino terminus (C. Ramilo et al., unpublished results). 

There are four disulfide bonds in short-chain (Type I) neurotoxins. This means that there are eight half-cystines. However, all Hydrophiinae toxins have nine halfcystines with one cysteine residue. An extra cysteine residue can be readily detected from the Raman spectrum as the sulfhydryl group shows a distinct S-H stretching vibration at 2578 cm" Some Laticaudinae toxins do not have a free cysteine residue as in the cases of L. laticaudata and L. semifasciata toxins. In long toxins (Type II) there are five disulfide bonds (Table III). 

The fast interaction of O2 with Fe(II)-cysteine complexes to give an oxygen adduct which rapidly undergoes one-electron breakdown to an Fe(III)-cysteine complex and -OJ has been examined by stopped-flow spectrophotometry at 570 nm . Subsequent decomposition of the Fe(IlI) complex to yield Fe(II) and the disulphide, cystine, was much slower. Both mono- and bis-complexes of Fe(Il) are involved and the reaction is first-order in both Fe(II) complex and O2 k (mono) = (5 +1) x 10 l.mole ksec" and k (bis) = (2 0.5) x lO l.mole . sec at 25 °C, corresponding to factors of 10 and 10 times faster than the analogous reactions with sulphosalicylic acid complexes of Fe(II), a feature attributed to Fe(ll)-S bonding in the cysteine complexes. ... 

However, this is not so easy without the tertiary structure of the enzyme. The possible clues are the homology search with functionally resembling enzymes and computer simulation of the tert-structure of the enzyme. The characteristic features of AMDase are (i) the reaction proceeds via an enolate-type transition state, (ii) the cysteine residue plays an essential role and (iii) the reaction involves an inversion of configuration on the a-carbon of the carboxyl group. 

If the injected acid itself contains iron (III), a precipitation of the asphaltic products can occur when it comes in contact with certain crude oils. This leads to practically irreversible damage of the zone treated. The amount of precipitate generally increases with the strength and concentration of the acid. Certain organic sulfur compounds, such as ammonium thioglycolate, mercaptoethanol, cysteamine, thioglycerol, cysteine, and thiolactic acid [581], can reduce the iron (HI). 

---