Cystine, oxidation

The reduction of the 2 -hydroxyl group in the ribose ring is coupled to the cysteine-to-cystine oxidation occurring in the Bt subunit. This process cannot occur directly and other intermediates are necessary, with NADPH as the final reductant. Reduced thioredoxin (or glutaredoxin) transfers electrons to an enzyme disulfide bridge, which in turn reduces the tyrosine radical which then interacts with the 2 -OH group. Little is known about the way in which the 2 -OH group is activated... 

Reaction mixtures were prepared by mechanical dispersion of the thiol (200 mg g ) on the activated support. Water (0.5 mL g-1) was added and the mixture was carefully mixed until an homogeneous (hydrated) loose solid was obtained. This solid was left at room temperature or heated in an open vessel for the indicated time. Products were eluted from the support either with diluted hydrochloric acid (cystine, oxidized glutathione, penicylamine) or methanol (tV-acetylcystine, cystine methyl ester). The solution was decolorized by addition of activated carbon, filtered and evaporated. 

Thioredoxin is a protein of 12,000 Da that can donate two electrons by the oxidation of two cysteine sulfhydryl groups to cystine oxidized thioredoxin is reduced by NADPH ... 

Cystine oxidation products from peroxide bleaching —CH—CH2—S—SO—CH2—CH— cystine monoxide... 

Since the bleaching of human hair is carried out in an aqueous alkaline oxidizing medium, hydrolysis of the cystine oxide intermediates (Figure... 

Zahn and co-workers [2], using two-dimensional gel electrophoresis, separated up to 62 isolated protein spots from human hair. From the fluoro-gram of bleached hair, these scientists identified cystine oxides (monoxide and dioxide). Although the exact quantities of these intermediate oxidation products versus cysteic acid were not reported, the quantities were indicated to be small relative to the cysteic acid content [2]. 

To summarize, sulfonic acid is the principal established end product of the oxidative cleavage of the disulhde bond from the chemical bleaching of human hair with current hair bleach products [3,9]. The mercaptan content of bleached hair is lower than that of unbleached hair [4], The intermediate oxidation products of cystine (i.e., the disulhde monoxide, dioxide, trioxide, and tetroxide) do not exist as signihcant end products of hair bleaching using today s commercial bleach products [3,6,9]. Nevertheless, evidence has been presented demonstrating low levels of cystine oxides in bleached hair [2],... 

Oxidized L-cysteine. See L-Cystine Oxidized keratin Synonyms Keratin, oxidized Definition Material derived chemically from keratin by oxidation with hydrogen peroxide Uses Hair conditioner, skin conditioner in cosmetics... 

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