Cysteine products derived from

Two of the nonessential amino acids, tyrosine and cysteine, are derived from essential amino acids and may be considered to be breakdown products, as they are intermediates in the normal degradation of these amino acids. Provided sufficient of the two essential amino acids phenylalanine and methionine are available through the diet, net synthesis of tyrosine and cysteine can occur. 

HNE-Modified Protein This arises by the covalent binding of HNE, an endogenously generated major lipid peroxidation product derived from breakdown of lipids containing u)-6 fatty acids (lin-oleic and arachidonic acid), to nucleophilic sites in the given protein. HNE reacts with the side chains of cysteine (Cys, C), histidine (His, H), and lysine (Lys, K) in an order of reactivity Cys His > Lys. 

Sulfuric acid may be reduced to the level of sulfide and is then an important building stone of L-cysteine (see below). L-Cysteine, (S)- x-amino-/ -thiolpropionic acid, is one of the most important sulfur-containing substances in primary metabolism. The secondary products derived from L-cysteine may contain the sulfur in different states of oxidation. Of importance are sulfides (—S—), disulfides (—S—S— ), sulfenic acids (—S—OH), sulfoxides (—SO— ), sulfinic acids (—SO—OH) and sulfonic acids (—SO2—OH). 

Sulfuric acid esters with alcoholic or phenolic hydroxy groups, the mixed anhydrides adenosine-5 -sulfatophosphate and its 3 -phosphorylated derivative, as well as secondary products derived from L-cysteine occur in microorganisms, plants and animals. Sulfuric acid amides, e.g., the glucosinolates (D 9.4), are formed in certain plants. 

Secondary Products Derived from ASP, PAPS, and l-Cysteine... 

In NRPs and hybrid NRP-PK natural products, the heterocycles oxazole and thiazole are derived from serine and cysteine amino acids respectively. For their creation, a cyclization (or Cy) domain is responsible for nucleophilic attack of the side-chain heteroatom within a dipeptide upon the amide carbonyl joining the amino acids [61]. Once the cyclic moiety is formed, the ring may be further oxidized, to form the oxazoline/thiazoline, or reduced, to form oxazolidine/thiazolidine (Figure 13.20). For substituted oxazoles and thiazoles, such as those... 

TES-32 is the most abundant single protein product secreted by the parasite. It is also heavily labelled by surface iodination of live larvae (Maizels et al., 1984, 1987), and is known by monoclonal antibody reactivity to be expressed in the cuticular matrix of the larval parasite (Page et al, 1992a). TES-32 was cloned by matching peptide sequence derived from gel-purified protein to an expressed sequence tag (EST) dataset of randomly selected clones from a larval cDNA library (Loukas et al., 1999). Because of the high level of expression of TES-32 mRNA, clones encoding this protein were repeatedly sequenced and deposited in the dataset (Tetteh et al., 1999). Full sequence determination showed a major domain with similarity to mammalian C-type (calcium-dependent) lectins (C-TLs), together with shorter N-terminal tracts rich in cysteine and threonine residues. Native TES-32 was then shown to bind to immobilized monosaccharides in a calcium-dependent manner (Loukas et al., 1999). 

Perhaps more significantly they were also able to isolate a polar, water-soluble compound that they believed was 55 in which the cysteine residue had been incorporated into the artemisinin backbone. The broadness of the signals in the proton NMR spectrum made characterization problematic, but treatment of 55 with acetic anhydride afforded 56, which was fully characterized (Scheme 16A). More recently, the same group has isolated and characterized another product from artemether. Adduct 57 was derived from the C4 secondary radical and cysteine (Scheme 16B). 

In this approach cysteine (19) was reduced to Cys(ol) (20) which was isolated as the triacetyl derivative 21. This compound was hydrolyzed with hydrochloric acid, the resulting hydrochloride 22 treated with 3 equivalents of NaOEt followed by addition of the a-bromo acid 24 derived from D-leucine (23). The resulting product 25 can then be /V-Boc-protected to yield the pseudodipeptide in a form suitable for solid-phase chain elongation. 

The kinetics of reaction of a number of A-nitrosothiols (334) in water with mercury(II) salts have been reported. Reaction is first order in both reactants and the products are nitrous acid and the corresponding thiol-Hg2+ complex. The mechanism involves slow attack by water at the nitrogen atom in the complex.300 The same group has also studied the copper(II)-catalysed decomposition of the, -nitrosothiols derived from penicillamine, cysteamine, thiomalic acid, A -acetylpenicillaminc, and cysteine.301... 

Schrauzer has shown that compounds derived from molyb-denum(V)-cysteine derivatives also catalyze the reduction of dinitrogen. Subsidiary experiments confirm that the active species contain molybdenumdV) rather than molybdenum Ill), the latter tending to lead to the production of dihydrogen (279). Molybdenum isonitrile derivatives can also lead to dinitrogen-reduction catalysis (252). These systems are very difficult to analyze, and they often work best at low molybdenum concentrations (<10 3 M). The intermediates cannot be isolated or detected directly. Their nature must be inferred on the basis of circumstantial evidence, and this is sometimes difficult to interpret. 

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