Cysteine reaction

If the medium becomes more dilute, the rate of Amadori compoimd formation is in general drastically reduced. However, this does not apply to the cysteine reaction. As a consequence, cysteine becomes clearly the most reactive amino acid in dilute neutral media (Table II). A possible explanation for the relatively high reactivity of cysteine in dilute aqueous systems is the high concentration of the cysteine-sugar condensation products thanks to the assistance by the thiol group. Therefore, in dilute systems the concentration of the Schiff s base of cysteine 6 will be much higher than the concentrations of the corresponding Schiff s bases of the other amino acids. 

Attachment to Sulfur Groups. Of all the amino acids, the two most reactive in solution toward the electron are cystine and cysteine. Reaction with the former leads to the disulfide anion radical,... 

This rate law and the mechanism proposed to explain it are analogous to that given for the chromate-cysteine reaction carried out in acid media namely, the rapid formation of a thioester complex followed by its reduction via two alternative pathways, one involving a proton and the other a second molecule of penicillamine This is illustrated as follows ... 

The situation is therefore similar to that in the synthesis of poly(ethylene terephthalate) by transesterification. Furthermore, the molecular weight can be increased by oxidation of the —SNa end groups in analogy to the cystine-cysteine reaction ... 

H atoms have been reported to react with cystine with a rate constant of 5 X10 lmol"7s-7 and to produce cysteine , reaction (23). A transient... 

At mercury electrodes Lee reported that cystine dissolved in perchloric acid was reduced to cysteine (Reaction 5.3) at a potential of —0.43 V, but that there was also evidence of the transient formation of mercurous cysteinate as a reaction... 

Chemical degradation of amino acids such as glutamin, cysteine reaction of amino-acids with glucose (Maillard reaction)... 

Cyclopropyl amines as inhibitors, 38 Cymarin, 75, 524-526, 529 Cystathionase, 31, 32, 163, 445 Cysteine, reactions with bromoacetyl-pyridine, 150... 

Perhaps the main disadvantage of the diphenylamine reaction for de-soxypentose is the lack of sensitivity. In addition, interference in the test by some substances has been shown by certain investigators (17,21,23,44). Three recently proposed methods deserve serious consideration. Cohen (23) has developed a color reaction with tryptophane, while Stumpf (98) has standardized the cysteine reaction originally proposed by Dische (40). Both methods are accurate in the range of 50-500 / g. of DNA. Ceriotti (21) has developed a micromethod (2.5-15 /xg. of DNA) using the reaction of indole with DNA, followed by extraction of the yellow pigment with chloroform. 

Sources.—Glutathione was isolated in 1921 from yeast, muscle, and mammalian liver by Hopkins, and identified as the compound responsible for Morner s cysteine reaction—the development of a violet colour when the tissue is treated with sodium nitroprusside (nitroferricyanide) and ammonium hydroxide. The reaction is specific for the ihiol or svlphydryl group, —SH, and is given by most... 

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