Cysteine sulfate

Cysteine. In animals, cysteine is converted to pyruvate by several pathways. In the principal pathway, the conversion occurs in three steps. Initially, cysteine is oxidized to cysteine sulfate. Pyruvate is produced after a transamination and a desulfuration reaction. 

Sulfur. Sulfur is present in every cell in the body, primarily in proteins containing the amino acids methionine, cystine, and cysteine. Inorganic sulfates and sulfides occur in small amounts relative to total body sulfur, but the compounds that contain them are important to metaboHsm (45,46). Sulfur intake is thought to be adequate if protein intake is adequate and sulfur deficiency has not been reported. Common food sources rich in sulfur are Hsted in Table 6. 

D. desulfuricans is able to grow on nitrate, inducing two enzymes that responsible for the steps of conversion of nitrate to nitrite (nitrate reductase-NAP), which is an iron-sulfur Mo-containing enzyme, and that for conversion of nitrite to ammonia (nitrite reduc-tase-NIR), which is a heme-containing enzyme. Nitrate reductase from D. desulfuricans is the only characterized enzyme isolated from a sulfate reducer that has this function. The enzyme is a monomer of 74 kDa and contains two MGD bound to a molybdenum and one [4Fe-4S] center (228, 229) in a single polypeptide chain of 753 amino acids. FXAFS data on the native nitrate reductase show that besides the two pterins coordinated to the molybdenum, there is a cysteine and a nonsulfur ligand, probably a Mo-OH (G. N. George, personal communication). 

CS-PG, chondroitin sulfate-proteoglycan these are similar to the dermatan sulfate PGs (DS-PGs) of cartilage ffable 48-11). SPARC, secreted protein acidic and rich in cysteine. 

However, Phinney (8) has suggested on the basis of experiments with mutants of Neurospora that the biosynthesis of cysteine involves the coupling of sulfate with an organic compound (presumably cysteine sulfinic acid) followed by reduction to sulfide. He noted also that sulfate may be reduced stepwise to sulfide and may then enter the protein as such. But he observed this process proceeds less readily than when sulfate combines first with protein. 

The second important issue related to commercial use of desulfurization biocatalysts is their inhibition by sulfate. The sulfur repression mechanism in most Rhodococcus species limits their use or activity in presence of sulfate- and sulfur-containing amino-acids such as cysteine, methionine, etc. To alleviate this problem, expression of the dsz genes under the control of alternate promoters has been investigated. 

Another report describing an approach to achieve alleviation of sulfur repression came from the Matsui research group. The dsz genes were cloned into a strain Rhodococcus sp. strain T09 under the promoter rrn of the strain T09 using a Rhodococcus-E. coli shuttle vector [214,215], This resulted in a strain which desulfurized DBT to 2-HBP in presence of sulfate, cysteine, or methionine. Similar approach was also used by Kurane to construct a gene expressing dszA-D enzymes, which eliminate the sulfate inhibition effects [216],... 

Figure 28.21 The reactions of R u (11) pby 3 + are catalyzed by light at 452 nm that begins by forming an excited state intermediate. In the presence of persulfate, a sulfate radical is formed concomitant with the oxidative product Ru(III)bpy33+. This form of the chelate is able to catalyze the formation of a radical on a tyrosine phenolic ring that can react along with the sulfate radical either with a nucleophile, such as a cysteine thiol, or with another tyrosine side chain to form a covalent linkage. The result of this reaction cascade is to cause protein crosslinks to form when a sample containing these components is irradiated with light.

Hydrogen sulfide is a well known general metabolite produced on sulfate reduction by certain bacteria. Moreover, organic forms of sulfur can give rise to HS , hence H2S in certain bacteria. Thus, cysteine desulfhydrase (EC 4.4.1.1, cystathionine y-lyase) converts L-cysteine to H2S, pyruvate, and NH3. This enzyme shows a requirement for pyridoxal phosphate and the unstable ami-noacrylic acid is an intermediate (Equation 1) in the reaction ... 

Sullivan reaction org chem The formation of a red-brown color when cysteine is reacted with l,2-naphthoquinone-4-sodium sulfate in a highly alkaline reducing medium. sal-a-van re,ak-shan ) eulpho-See sulfo-. sal-fo )... 

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