Sulfhydryl-containing amino acid

Humans may be exposed to hydrogen sulfide both from its endogenous production or from exogenous sources. Most endogenous production apparently results from the metabolism of sulfhydryl-containing amino acids, e.g., cysteine, by bacteria present in both the intestinal tract and the mouth (Beauchamp et al. 1994 Tonzetich and Carpenter 1971) however, it is also produced in the brain and several smooth muscles, e.g., thoraic aorta, by enzymes found in these tissues (Abe and Kimura 1996 Hosoki et al. 1997). 

Rabenstein DL, Fairhurst MT (1975) Nuclear magnetic resonance studies of the solution chemistry of metal complexes. XL The binding of methylmercury by sulfhydryl-containing amino acids and by glutathione. J Am Chem Soc 97 2086-2092... 

Cysteine conjugates. Additional trapping experiments were carried out with stable isotope derivatives of acetylhydrazine and isopropylhydrazine and the sulfhydryl containing amino acid, cysteine. When an equimolar mixture of acetylhydrazine and tri-deuteroacetylhydrazine was incubated with rat liver microsomes. 

The equilibria of a series of sulfhydryl groups containing amino acids have been investigated (Mezyk 1995, 1996a,b), and details governing these equilibria are now reasonably well understood (Mezyk and Armstrong 1999). 

Cysteine, the only sulfhydryl (—SH)-containing amino acid of the 20 commonly found in proteins, has a chemical property not shared by the other 19. We learned in Section 3.9 that a sulfhydryl group can easily be oxidized to form a disulfide bond (—S—S—). Thus, two cysteine molecules react readily to form a disulfide compound called cystine. The disulfide, in turn, is easily converted to —SH groups by the action of reducing agents ... 

Another important natural fibrous material is wool. Wool is mainly made of proteins called keratins. Not a single kind, but several different keratins are involved acidic and basic keratins and keratin-associated proteins. Keratins are related to silk fibroin mentioned earlier. Both a-helix and P-pleated structures of keratin are involved. The keratin-associated proteins contain high level of the sulfur-containing amino acid, cysteine. The sulfhydryl (-SH) group of cysteine can readily be oxidized and combine with another sulfhydryl sulfur atom of another cysteine residue on another polypeptide. The result is the formation of sulfur-sulfur... 

The sulfur atom (with its polarizable or elastic electron cloud) is one of the best nucleophiles known and cysteine, like serine, can participate in a number of biochemical reations. Also, the sulfhydryl of cysteine is quite oxidizable to give rise to the disulfide, cystine. Another sulfur-containing amino acid is ... 

The amino acid residues in neurotoxins which are important for neurotoxic action are still not entirely clarified. Some neurotoxins contain one free SH group, while others do not. From this fact, it would be logical to assume the sulfhydryl group is not essential. This was actually proven to be the case. 

Aryl halide compounds such as fluorobenzene derivatives can be used to form covalent bonds with amine-containing molecules like proteins. The reactivity of aryl halides, however, is not totally specific for amines. Other nucleophiles such as thiol, imidazolyl, and phenolate groups of amino acid side chains also can react (Zahn and Meinhoffer, 1958). Conjugates formed with sulfhydryl groups are reversible by cleaving with an excess of thiol (Shaltiel, 1967). 

FIGURE 5.22 (A) Reaction of an Fmoc-amino acid with 2-chlorotrityl chloride resin.56 The ester bond formed is cleavable by the mild acid, which does not affect tert-butyl-based protectors. (B) Generation of a protected peptide containing cystine by detachment of a chain, deprotection of cysteine residues, and oxidation of the sulfhydryls by the reagent containing iodine. The cations produced are trapped by CF3CH2OH. 

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