1-Cystine

Human hair (Note i) is freed from foreign matter (Note 2), washed well with a lukewarm solution of soap (Note 3), then twice with cold distilled water, and dried. This washing removes the natural oils from the hair (Note 4). Two kilos of the dry, washed hair is pushed into a 12-I. round-bottom Pyrex flask, and 4 1. of 20 per cent hydrochloric acid (Note 5) is added. An air-cooled reflux condenser, consisting of a wide glass tube, is attached to the flask. The hair is hydrolyzed by heating on the steam bath (Note 6) until the biuret reaction is entirely negative this requires one hundred twenty to one hundred forty-four hours. 

The mixture is filtered hot and the insoluble residue is washed with distilled water. The total filtrate is now partially neutralized with 300 cc. of 40 per cent sodium hydroxide solution, while the mixture is well stirred and cooled, and then a saturated solution of 3750 g. of crystallized sodium acetate is added. The Congo Red test for mineral acid should then be entirely negative. Care must be taken not to make the solution alkaline with sodium hydroxide (Note 7). After standing for three days at room temperature, the precipitated cystine is filtered on a suction iunnel. This crude material, containing in addition to the 

Crude sheep s wool may also be employed, but the yield is not so high (about 2.6 per cent). 

Hair obtained from barber shops generally contains matches, paper, cigar and cigarette butts, and similar impurities which should be sorted out by hand as completely as possible. The other principal contamination is sand which causes little trouble and need not be removed. 

A high grade of soap should be employed. Hair kept in hot dilute sodium carbonate solution for one to two hours yields little or no cystine. 

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Fig. 2.1.2a-c A Urine amino acids in a patient with cystinuria assayed by an amino acid analyzer (AAA). The indicated peaks are 1 glycine, 2 cystine, 3 ammonia, 4 ornithine, 5 lysine, 6 arginine, i.s. internal standard (S-amino thyl-cysteine). Cystinuria treatment is best followed-up by analyzing an early morning urine specimen, which usually shows the highest amino acid concentrations. b-c see next page... 

Cysteine as cysteic acid, except for microbubble glycopeptide surfactant for which determined as 1/2 Cystine. 

The total half-cystine content of pig heart lipoamide dehydrogenase is 10 per FAD 6S). The basis for the protein quantitation has been discussed in Section II,C. Older data suggested that there were 2 cystine residues and 6 cysteine residues 83), but more recent data 61, 63) give strong evidence that the active center cystine residue is the only cystine residue. Only 7 thiols react with DTNB under denaturing conditions (dS) however, recalculation of data of Brown and Perham 86), taking... 

The absorption spectra of several cystine-containing peptides as obtained by Otey and Greenstein (1954) are shown in Fig. 3. Some nonadditivity of absorptivities is evident for example, the spectrum of l-cystinyl-L-cystine is obviously not simply the sum of 2 cystine spectra, even at wavelengths greater than 2500 A, where the disulfide group is the only significant chromophore. The question, What is a suitable model for cystine absorptivity in a protein is apparently farther from a satisfactory answer than is the parallel question for aromatic amino acid residues. 

Estimated as Ar-(dinitrophenyl)cysteic acid. As a maximum of 12.5 free sulfhy-dryl groups are found with p-(chloromercuri)benzoate, this value represents 12.5 cysteine and 2 cystine residues. Tryptophan was estimated spectrophotometrically. Not included in total. 

SLC3 (2) Cystine, dibasic, and neutral amino acid ATR, RBAT Kidney and intestine... 

As shown in Equations 1 and 2, cystine lyase produces cysteine, pyruvate, ammonia and sulfur from cystine. The cysteine is further acted upon to give pyruvate, hydrogen sulfide and ammonia. Hydrogen sulfide and ammonia formation probably account for the sulfhydryl compound and ammonia aromas detected in the unblanched sample. The pyruvic acid (at the pH of the samples) may account for the sour aroma detected in the unblanched sample, as well as samples treated with lyase and lipase separately. 

Sodium hydride in DMSO is an effective medium for the reduction of disulfide bonds in proteins under aprotic conditions. When the molar ratio of hydride to 1/2 cystine residues exceeds 2 1, essentially complete reduction of the disulfide bonds of bovine serum albumin is achieved. 

Cystine heart agar blood (CHAB) made of cystine heart agar (CHA Difco, Beckton Dickinson, Sparks, MD, USA) supplemented with 9% sheep blood. The sheep blood is chocolatized by adding it to autoclaved CHA before it cools below 75 °C. 

The nomenclature is not uniform. Some laboratories express their results as 1/2-cys-tinej 1 nmol 1/2-cystine/mg protein equals 0,5 nmol cystine/mg protein. 

Cystine was isolated from bladder calculi by Wolaston in 1810 and from horns by Moerner in 1899. Its content is high in keratins (9%). Cystine is very important since the peptide chains of many proteins are connected by two cysteine residues, i. e. by disulfide bonds. A certain conformation may be fixed within a single peptide chain by disulfide bonds. Most proteins contain 1-2% cystine. Although it is itself nonessential, cystine can partly replace methionine which is an essential amino acid. 

However, as mentioned above, hemerythrin of Sipunculus nudus contains 10 iron atoms and only 2 cystine residues per molecule of protein (Holleman and Biserte, 1958). If, according to Klotz s theory, only the iron atoms which are linked to the protein through -SH groups operate in the oxygenation reaction, most of the iron of Sipunculus hemerythrin would be inactive, in contrast with the data on the iron-oxygen ratio. 

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