Cystine and methionine

LPC Product Quality. Table 10 gives approximate analyses of several LPC products. Amino acid analyses of LPC products have been pubhshed including those from alfalfa, wheat leaf, barley, and lupin (101) soybean, sugar beet, and tobacco (102) Pro-Xan LPC products (100,103) and for a variety of other crop plants (104,105). The composition of LPCs varies widely depending on the raw materials and processes used. Amino acid profiles are generally satisfactory except for low sulfur amino acid contents, ie, cystine and methionine. 

Tonzetich J, Carpenter PAW. 1971. Production of volatile sulphur compounds from cysteine, cystine and methionine by human dental plaque. Arch Oral Biol 16 599-607. 

The XPS-spectrum of commercial papain desplays only a minor RSOJ and/or sulphate band above 168 eV. Essentially all sulphur has a 2p-binding energy level of 163.2 eV attributable to cystine and methionine sulphur (Fig. 3). 

SULFUR (In Biological Systems). Sulfur, in some form, is required by all living organisms. It is utilized in various oxidation stales, including sulfide, elemental sulfur, sulfite, sulfate, and thiosulfate by lower forms and in organic combinations by all. The more important sulfur-containing organic compounds include the amino acids (cysteine, cystine, and methionine, which are components of proteins) the vitamins thiamine and... 

DNA is typically surrounded by proteins, and the question obviously arises as to what extent they may contribute to a repair of DNA radicals. The G-+/G-radical has been generated in plasmid DNA in aqueous solution with the help of (SCN)2, and the formation of G lesions has been monitored as SSBs induced by the Fpg protein (Milligan et al. 2003). The repair of G-+/G by electron-donating amino acids has been studied. Most of these, notably tryptophan, were found to be quite reactive except for histidine and some derivatives of cystine and methionine (Table 12.23). 

The metabolism of cystine and methionine. Availability of methionine in supplementing a diet deficient in cystine. Ibid., 98, 465 (1932). With R. W. Jackson. 

Synthesis of sulfur amino acids from inorganic sulfate by ruminants. II. Synthesis of cystine and methionine from sodium sulfate by the goat and by the microorganisms of the rumen of the ewe. Arch. Biochem. Biophys., 33, 353... 

Sulfur metabolism of insects. I. Utilization of sulfate for formation of cystine and methionine by the German cockroach, Blatella germanica (L.). Contribs. Boyce Thompson Inst., 18, 109 (1955). With J. D. Hilchey, L. P. Miller, and R. M. Weed. 

The presence of sulfur is probably the result of sulfur oxides in the air combining with the silver. These oxides are present whenever fossil fuels are burned, and they readily attack silver. Researchers (5) have stated that sulfur in such metallic yarns is the result of the breakdown of the silk protein, fibroin. This occurrence, however, is unlikely because silk contains almost none of the two sulfur-containing amino acids, cystine and methionine (20). The exact source of the chlorine present in the sample is less easy to explain. It is present in most, though not all,... 

The ultraviolet absorption spectra of cysteine, cystine, and methionine are shown in Figs. 2, 3, and 11. The lowest energy (long-wave absorption band) transitions have been assigned (Mulliken, 1935 Walsh, 1953) as n — (f transitions. Transition assignments for disulfide spectra have been critically discussed in a recent paper by McGlynn et al. (1962). The... 

Underheating of whole soybean may fail to destroy the trypsin inhibitor and reduce urease and lipase activity, resulting in low protein efficiency for critical feeds. An underheated soybean meal greatly increases the need for vitamin D to prevent rickets in turkey poults. Overheating of whole soybeans tends to inactivate or destroy the essential amino acids lysine, cystine, and methionine and possibly others (31). 

This element is present in some enzymes when it is chemicaUy bonded to the amino acid cysteine and, to a lesser extent, cystine and methionine (all three of these are sulfur-containing amino acids). Sulfur and selenium seem to have an affinity for one another. Selenium is in certain hydrogenases in combina-... 

The protein is completely hydrolyzed by acid (6 N HCl, 24 hours or longer at 110°C, under vacuum or inert gas) to its constituent amino acids and the resultant hydrolysate is evaporated to dryness. The amino acid composition is determined on protein hydrolysates obtained after 24,48, and 72 hours of acid treatment. The content of amino acids with bulky aliphatic side chains such as isoleucine, leucine, and valine, which undergo slow hydrolysis, is calculated from an extrapolation of the hydrolysate data to infinite time. The content of hydroxyl-containing amino acids, which are slowly destroyed during hydrolysis, is obtained by a corresponding extrapolation to zero time. Since cysteine, cystine, and methionine residues are somewhat unstable to hydrolysis, these residues are oxidized to cysteic acid and methionine sulfone, respectively, with performic acid before quantitative analysis. Cysteine, or half-cystine, is quantitated as a derivative such as carboxymethyl cysteine after reduction and alkylation, a necessary prerequisite to subsequent sequence analysis. Tryptophan... 

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