Sulfhydiyl group

The sulfhydiyl group in cysteine can be selectively protected in the presence of the amino group by reaction with 2,4-dinitrophenol at pH 5-6. ... 

More recently, B. Goldstein and McDonagh demonstrated that the native protein fluorescence (280-nm excitation, 330-nm emission) of red-cell membranes exposed in vitro to ozone at 1 ppm was a somewhat more sensitive indicator of ozone effect than other characteristics measured in the same em, including oxidation of cell-membrane sulfhydiyl groups, loss of acetylcholinesterase activity, and formation of lipid peroxide breakdown products. 

Although a sulfhydiyl group generally is not converted to an 5-phenyi thioether, thiophenol can be used to introduce sulfur into molecules, and thus the phenyl group serves as a suitable protective group that can be removed by electrolysis (-2.7 V, DMF, R4N+X ). ... 

Sulfhydiyl groups meihimuzole. propylihiouracil, dicthylihiocoibomic acid... 

The high affinity of MeHg and mercuric Hg for sulfhydiyl groups is believed to be a major mechanism that underlies their toxicity. If those sidfhydiyl groups are in the active center of critical enzymes, severe inhibition of essential biochemical pathways occurs. 

Cysteine proteinases contain a catalytically active cysteine sulfhydiyl group (Cys-25) and a histidine group (His-159) within the active center of the enzyme [51]. Alkylation of the active-center sulfhydryl group renders the product inactive. The minimal reaction mechanism is represented in Figure 4 [52]. 

Lastly, cysteine, glycine, and proline exhibit special roles In proteins because of the unique properties of their side chains. The side chain of cysteine contains a reactive sulfhydiyl group (—SH), which can oxidize to form a covalent disulfide hond (—S—S—) to a second cysteine ... 

In proteins, three amino acids, tryptophan, tyrosine and phenylalanine, are responsible for the U.V. absorption, c in proteins is detemiined at the maximum (278 nm) (Fig. 1.13) and thus, concentrations of proteins are calculated by measuring the absorbance at this wavelength. Cystine and the ionized sulfhydryl groups of cysteine absorb also in this region but much weakly than the three aromatic amino acids. Ionization of the sulfhydiyl group induces an increase in the absorption and an appearance of a new peak around 240 nm. The imidazole group of histidine absorbs in the 185-220 nm region. Finally, important absorption of the peptide bonds occurs at 190 nm. 

Metal ions can also react with amino and sulfhydiyl groups of proteins involved in nucleic acid metabolism. This frequently results in an inhibition or dysfunction of the corresponding enzymes. By this metals can contribute in an indirect way to alterations in genetic information by affecting replication fidelity. Metal compounds can also cause DNA strand breaks indirectly, e.g., by causing depurination of DNA or via their involvement in generating oxygen free radicals. 

The E. coli enzyme has been purified to homogeneity the molecular weight is about 66,000 and the enzyme consists of two identical or very similar polypeptide chains. The amino acid composition of the enzyme has been determined (13). It has been proposed that each of the two thioredoxin reductase subunits has an active center containing one FAD molecule and one disulfide linkage, both of which act as oxidation-reduction acceptors during catalysis (13). As well, thioredoxin reductase contains four additional sulfhydiyl groups per molecule (presumably, two per subunit), but these do not participate in the catalytic function. The amino acid sequence at the active site of the E. coii thioredoxin reductase has been determined to be as follows (14) ... 

Mercaptan (Section 10.9B) A common name for a thiol that is, any compound that contains an -SH (sulfhydiyl) group. 

Privat, R. Jaubert, J.N. Mutelet, F. (2008b). Addition of the sulfhydiyl group (-SH) to the PPR78 model (Predictive 1978, Peng-Robinson EoS with temperature dependent k calculated through a group contribution method). /, Chem. Thermodyn., VoL 40, No.9, pp. 1331-1341... 

Metallothioneins of mammals are single-stranded low molecular proteins with 61 - 68 amino acids in the structure. Cysteine accounts for one third of amino acid moieties eysteine moieties are located in the conservative sequences such as cys-x-cys, cys-x-y-cys and cys-cys (x and y are amino acids different from cysteine). Metal ions are boimd to sulfhydiyl groups of cysteine moieties that create tetraedric conformation of thiolated clusters in the ease of divalent ions [12]. MT has the highest affinity to Cu (stability constant lO - lO ), then to Cd (lO - lO ) and Zn (lO " - lO") and it is not able to bind Cu. Eighteen metal ions that can be bound by MT have been shown however, only Cu", Cd, Pb, Hg, Ag and Bi are able to displace boimded Zn from the structure of MT. Overall, it can coordinate up to 12 mono- or 7 divalent ions. Its tertiary structure is based on the presence of two domains, a and (3 (Fig. 1). a-domain (C-terminal) is more stable and contains four binding sites for divalent ions of heavy metals, P-domain (N-terminal) can bind three divalent metal ions [13]. 

The observations are in complete accord with the view that a free sulfhydiyl group or groups is required for proteolytic activity. Papain is activated by agents capable of reducing disulfides and is Inactivated by agents which will oxidize free thiols. The susceptibility of active papain to heavy metal ions is to be expected since sulf-hydryl compounds have a high affinity for such ions. It is important to emphasize that, although papain requires activation, the continued presence of the activator is not required. This is the most conclusive proof that cysteine, HCN, etc. do not function as coenzymes. 

Unsaturated lactones react with sulfhydiyl groups (48) to add the RS— to the carbon to the lactone in and lactones. Substitu-... 

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