Methionine cystine from

As constituents of proteins the amino-acids are important constituents of the food of animals. Certain amino-acids can be made in the body from ammonia and non-nitrogenous sources others can be made from other amino-acids, e.g. tyrosine from phenylalanine and cystine from methionine, but many are essential ingredients of the diet. The list of essential amino-acids depends partly on the species. See also peptides and proteins. 

Thiophenes are extremely important in flavor and are responsible for the mild sulfurous odor of cooked meat. Numerous other thiophenes have been identified during heating of meat or meat constituents. The sulfur in thiophene may be derived from amino acids (cysteine, cystine, methionine) or from vitamin. ... 

Radioactive L-cystathionine (10) (765 mg.) containing 6.85 x 106 counts per minute of S35 was fed to the human cystinuric patient who had served previously as the subject in an experiment demonstrating the formation of cystine from sulfur-labeled methionine (11). The same precautions were followed with regard to human experimentation involving radioactive material as in the latter experiment. After the feeding of the cystathionine, 24-hour urine specimens were collected for 3 days and sulfur distributions were determined by the titrimetric method of Fiske (6). Cystine determinations were carried out by the procedure of Sullivan, Hess, and Howard (12). 

Our findings in this study are in harmony with the concept that L-cystathionine is an intermediate in the formation of cystine from methionine in man. Direct evidence for the existence of cystathionine in man was provided by the demonstration by Tallan, Moore, and Stein (13) of the occurrence of L-cystathionine in extracts of human brain. Moreover, cases of human cystathioninuria have been reported by Harris, Penrose, and Thomas (9) and by Frimpter, Haymovitz, and Horwith (8). The latter authors have also stated that an increased renal clearance of cystathionine is not observed in cystinuria. It is of considerable interest, however, that the mixed disulfide of L-cysteine and L-homo-... 

Children do not grow normally if they lack taurine, arge-nine, and cystine. Older children and adults can make cystine from the amino acid methionine. 

Certain early speculations about the mechanism of formation of cystine from methionine contained shrewd inferences ivhich later work has shown to be correct in part. Brand and co-workers- first postulated transfer of the sulfur from a 4-carbon to a 3-carbon chain. These workers suggested that homocysteine condensed with a-aminoacrylic acid to form an intermediate compound which was cleaved to yield cysteine. Toennies suggested the direct transsulfuration between methionine... 

The evidence given above for the key role of cystathionine in the transsulfuration reaction to form cystine from methionine would be measurably strengthened by proof of the occurrence of this compound as a product of the metabolism of methionine. In Neurospora cystathionine has been isolated from the culture medium of certain methionineless mutants and shown to be a step in the conversion of cysteine to methio-... 

Amelogenin proteins are present in high proportions in the developing enamel of mammals. The amino acid composition of amelogenins from various species is shown in Table 32.4 from which it can be seen that, as compared with most proteins, they have a high content of proline, glutamic acid, histidine and methionine. Cystine, hydroxylysine and hydroxyproline are completely lacking or present in minimal amounts. 

TABLE 8.3.4. Near-Infrared Cross-Validation Statistics for Methionine (Met), Met - -Cys (Methionine - - Cystine), Cystine (Cys), and Lysine (Lys) in Livestock Animal By-Products Sourced from Different Authors... 

Hydrogenolysis with Raney nickel of L-cystine and n-methionine respectively (Mozingo, Wolf, Harris and Fokera, 1943. Fonken and Mozingo, 1946) has confirmed the configuration assigned to natural cystine by Fischer and has also demonstrated that the methionine obtained from proteins is configurationally related to L(-h)a-amino-butyric acid. 

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. 

The sulfur amino acid content of soy protein can be enhanced by preparing plasteins from soy protein hydrolysate and sources of methionine or cystine, such as ovalbumin hydrolysate (plastein AB), wool keratin hydrolysate (plastein AC), or L-methionine ethyl ester [3082-77-7] (alkaU saponified plastein) (153). Typical PER values for a 1 2 mixture of plastein AC and soybean, and a 1 3 mixture of alkah-saponified plastein and soybean protein, were 2.86 and 3.38, respectively, as compared with 1.28 for the soy protein hydrolysate and 2.40 for casein. 

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. 

Investigations of the effects of UV- and hypochlorite-induced oxidative modification of 20 amino acids and human serum albumin (HSA) on their antiradical properties showed unexpected results [36], Seven amino acids (cystine, histidine, methionine, phenylalanine, serine, tryptophan, and tyrosine) and HSA developed ACW following oxidation (see examples in Fig. 14). The fresh (produced in 1998) HSA from Serva had no antiradical capacity, but it acquired this quality during irradiation. The out-of-date HSA sample (Dessau, GDR, 1987, expiration date 7/1/1992) showed a remarkable ACW even in an unirradiated state. 

As early as 1905 Abderhalden (Al) isolated from the hydrolyzate of the nondiffusible fraction of human urine four amino acids, i.e., leucine, alanine, glycine, and glutamic acid, and detected two others phenylalanine and aspartic acid. Some amino acids derived from this fraction have been quantitatively determined by Albanese et al. (A3) who found in the amount of the nondiffusible fraction corresponding to one liter of urine as much as 32.8 mg tryptophan, 18.0 mg phenylalanine, 16.2 mg methionine, 15.2 mg cystine, 13.1 mg arginine, 6.7 mg histidine, and 3.9 mg tyrosine. 

By the 1930s many workers had shown that nutritionally inadequate proteins, such as zein from maize, could be effective as a source of nitrogen if supplemented by additional amino acids (for zein, tryptophan). Even if it contained all the essential amino acids, the amount of protein in the diet influenced the results. Osbome and Mendel found that if the diet contained 18% by weight casein, which is low in cystine, young rats grew, but if the amount of protein was diminished, added cystine was required to offset the relative deficiency of this amino acid. Later, after methionine had been discovered, it was shown to replace the need for cystine. 

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