Cysteine , isolation

It is possible that racemization of some of the amiiio aeids, such as cystine, serine, and threonine, occurs during extraction and accounts for some of the complexity of wool protein fractions (Lindley, unpublished observations, 1962). Performic acid, however, used in the preparation of the keratoses did not produce racemization in proteins (Hill and Smith, 1957). It has not proved possible to solve uneciuivocally the problem of whether or not the reduction and alkylation pi oceduros used in the preparation of SCM kerateiues cause racemization. Lindley (unpublished, 1961) has shown that S -carboxymethyl cysteine isolated from acid hydrolyzates of SCM kerateines is partially racemized as measured both by direct optical rotation procedures and also by the use of a C-S lyase enzyme which is specihe for the n-form (Schwinuner and Kjaer, 1960). Control experiments showed, however, that L-S-carboxymethyl cysteine itself is partially racemized on refluxing with 5 N acid, and when allowance was made for this it appeared that the amount of racemization attributable to the reduction and alkylation procedures was small (less than 5 %) even when the most drastic conditions (pH 12.5 and 50°C) were used to prepare the SCM kerateines. Since S-carboxymethyl cysteine in peptide combination may well racemize more readily on acid hydrolysis than does the free amino acid, even this may be an over-estimate, and it would seem unlikely therefore that racemization is a serious problem in SCM kerateines as presently prepared. 

Human hair is a good source of cystine, the disulfide dimer of cysteine. Hair is boiled with aqueous HCI and HCO2H for a day, the solution concentrated, and a large amount of sodium acetate added. About 5% of the hair by weight crystallizes out as pure cystine [a]c -216. How does the process work Why is such a high proportion of hair cystine Why is no cysteine isolated by this process Make a drawing of cystine to show why it is chiral. How would you convert the cystine to cysteine ... 

Production by Isolation. Natural cysteine and cystine have been manufactured by hydrolysis and isolation from keratin protein, eg, hair and feathers. Today the principal manufacturing of cysteine depends on enzymatic production that was developed in the 1970s (213). 

Cysteine [52-90 ] is a thiol-bearing amino acid which is readily isolated from the hydrolysis of protein. There ate only small amounts of cysteine and its disulfide, cystine, in living tissue (7). Glutathione [70-18-8] contains a mercaptomethyl group, HSCH2, and is a commonly found tripeptide in plants and animals. Coenzyme A [85-61-0] is another naturally occurring thiol that plays a central role in the synthesis and degradation of fatty acids. 

Reactions between A -(l-chloroalkyl)pyridinium chlorides 33 and amino acids in organic solvents have a low synthetic value because of the low solubility of the amine partner. A special protocol has been designed and tested in order to circumvent this drawback. Soon after the preparation of the salt, an aqueous solution of the amino acid was introduced in the reaction medium and the two-phase system obtained was heated under reflux for several hours. However, this was not too successful because sulfur dioxide, evolved during the preparation of the salt, was converted into sulfite that acted as an 5-nucleophile. As a result, A -(l-sulfonatoalkyl)pyridinium betaines such as 53 were obtained (Section IV,B,3) (97BSB383). To avoid the formation of such betaines, the salts 33 were isolated and reacted with an aqueous solution of L-cysteine (80) to afford thiazolidine-4-carboxylic acids hydrochlorides 81 (60-80% yields). 

In the rosary pea Abrus precatorius L. Trigollenine as well as its gallic acid ester Precatorine (209) is found (71P195) (Scheme 69). 1-Carboxymethyl-nicotinic acid (210) was isolated as a colorless solid from the marine sponge Anthosigmella cf. raromicrosclera as a cysteine protease inhibitor (98JNP671). This compound was first synthesized in 1991. The sodium... 

More recently, miraziridine A (113) was isolated from a marine sponge related to Theonella mirabilis and shown to inhibit the cysteine protease cathepsin B. It has been shown that the aziridine ring plays a key role in this biological activity and gives rise to irreversible inhibition of cathepsins B and L, presumably through... 

Of the twenty amino acids that are normally found in proteins, only two contain sulfur, cysteine and methionine. Cysteine has long been recognized as being easily oxidized and this oxidation is associated with the loss of biological activity of many proteins. In recent years, it has been shown that methionine also shares these characteristics. Methionine was first isolated by Mueller19 and was one of the last amino acids discovered. Its structure was later proven to be y-methylthio-a-aminobutyric acid by Barger and Coyne20 who named the amino acid methionine as a contraction for its chemical name. 

Proteolytic enzyme from the latex of Carica papaya with an approximate molecular weight of 27000. It is differentiated from papain in electrophoresis behavior, in solubility and in substrate specifity. Isolation by acidify of papaya-latex with HCl, salting out with NaCl and following chromatographic purification. The formulation contains L-cysteine as reducing agent. 

In 1984, the first methanogenic CODH was isolated from Methano-sarcina barkeri (138) and was shown to consist of a complex of the a and e subunits, with an apparent molecular mass of 232 kDa. Similar results have been found for other methanogenic CODH preparations (139-143). CODH activity must reside in the a subunit of the methanogenic enzyme, since the e subunit lacks cysteine residues and could... 

First isolated from D. desulfuricans (28), desulfoferrodoxin (Dfe) was also isolated from D. vulgaris (29). D is a 28-kDa homodimer that contains two monomeric iron centers per protein. These iron centers were extensively characterized by UV/visible, EPR, resonance Raman, and Mossbauer spectroscopies (30). The data obtained were consistent with the presence of one Dx-like center (center I) and another monomeric iron center with higher coordination number (penta or hexacoordinate), with 0/N ligands and one or two cysteine residues (center II). Comparison of known Dfx sequences led to the conclusion that only five cysteines were conserved, and that only one of them could be a ligand of center II (31). 

The ferredoxins isolated from D. gigas have been quite extensively studied by different experimental approaches and spectroscopic techniques and will be used here as a reference system. Ferredoxin I D. gigas Fdl) and ferredoxin II (D. gigas Fdll) (60-62) are composed of the same polypeptide chain (58 amino acids, 6 cysteines) (63). D. gigas Fdl is a dimer and contains a single [4Fe-4S], whereas the same monomeric unit of the tetrameric D. gigas Fdll contains a single [3Fe-4S] ° cluster. 

Two ferredoxins have been isolated from Desulfomicrobium bacula-tum (Dsm. baculatum) strain Norway 4 (64, 65). Dsm. baculatum ferredoxin I (59 amino acids, 6 cysteines) has one conventional [4Fe-cluster. Dsm. baculatum Fdll, the most acidic, is very unstable toward oxygen exposure and contains 2 X [4Fe-4S] cores in a polypeptide chain of 59 amino acids and 8 cysteines (66, 67). 

Three ferredoxins were isolated and characterized fromZ). africanus. The proteins are dimers of subunits with a molecular mass of circa 6 kDa. D. africanus Fdl contains a single [4Fe-4S] center bound to a polypeptide structure of 60 amino acids with only 4 cysteines. This is the minimal requirement for [4Fe-4S] cluster binding. D. africanus Fdll is a minor component, not so well characterized, and seems to contain a [4Fe-4S] center (68, 69). Fdlll of this strain is a dimer containing 61 amino acids and 7 cysteine residues per subunit. The protein contains a [3Fe-4S] and a [4Fe-4S] cluster (70-72). 

Two ferredoxins were isolated and purified from D. vulgaris Miyazaki. Fdl, the major form, contains two redox centers with distinct behavior and a high sequence homology to D. africanus Fdlll (73). The protein is a dimer of a polypeptide chain of 61 amino acids with 7 cysteines. D. vulgaris Miyazaki Fdll is a dimer of 63 amino acids, containing 7 cysteines but only one [4Fe-4S] cluster (73-75). 

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). 

On several occasions the product isolated by the submitters was contaminated with L-cystine dihydrochloride, which was not easily removed by recrystallization. In this event the product was converted to the zwitterionic form and recrystallized in the following manner. The pH of a solution of the product in water was adjusted to 6 with aqueous 2.5N potassium hydroxide. The neutralized solution was evaporated to dryness under reduced pressure at ca. 40°. The residue was dissolved in a minimum amount of hot water, and two volumes of 95% ethanol were added to precipitate S-acetamidomethyl-L-cysteine monohydrate, dec. 187°, [a] 9 — 42.5° (c = 1, water). 

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). 

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