Cystine sulphite with

The sulphite aftertreatment is particularly important with permonosulphuric acid treatment. Evidence for the underlying mechanism is available from analysis of sulphur oxidation products formed in the various processes (Table 10.34). It is evident from these results that the concentration of RSS()5 anionic groups necessary to change the hydration of the fibre surface is achieved by the reaction of bisulphite with cystine monoxide residues to give the required cysteine-S-sulphonate groups [311]. 

EMPA-Methode (6) cystine with sulphite, colori- peroxide, reducing agents ... 

Incubation of embrionic calf liver with 35S-labelled sodium sulphite, sodium pyruvate and sodium glutamate at 38 °C under nitrogen resulted in formation of 35S-cysteinesulphinic acid133,134. 35S-hypotaurine has also been isolated, but taurine-35S and cystine-35S have not been found. In the presence of serine, the yield of 35S-cysteinesulphinic acid was smaller. Organic 35S compounds without amino groups have also been formed in the same experiment. In the conditions employed in this bioexperiment cysteinesulphinic acid is not reduced to cystine-3 5S, although such reduction was found possible in vivo. 

The method was also used for the determination of cysteine and glutathi but its application presents, mainly in biological materials, the doubts expressed in the previous paragraphs. For the determination of cystine a method is employed based on the reduction of cystine in an acidic medium with sodium amalgam or on the reaction with sulphite at pH 8-12 according to equation ... 

Procedure. Deoxygenate 25-100 ml. of 0-05 n ammonia in the titration cell and add a sample of 4 X 10 M to 1 X 10 M cystine or cysteine. Make the solution O l m to sodium sulphite and carry out the titration with a 0-01 M solution of divalent copper which is preferably prepared from metallic copper. Measure the current at —0-4 V with a rotating platinum electrode. The titration curve obtained should be of the form given in Fig. 47. 

Cystine has also been determined in wool using a polarometric titration< based on the principle that sulphite reacts with... 

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