The Inoorporation of [35s]Oysteine into the Proteins of Dough by Disulphide-Sulphydryl Interohange

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Abstract
[35S] Cysteine was added, during mixing, to doughs made from wheat flour, in amounts which did not significantly affect the level of endogenous diffusible sulphydryl compounds in flour and which produced no change in the Theological properties of the dough. The doughs were fractionated by ultracentrifugation and analysis of the distribution of the isotope in the dough fractions demonstrated that [35S] cysteine was bound to both soluble and gluten proteins by disulphide bonds. [14C] Leucine did not become bound to the fractions of dough under the same conditions. Incorporation of cysteine into dough was increased in the absence of air, suggesting disulphide-sulphydryl exchange rather than oxidation as the mode of incorporation. The amount of isotope bound to protein was also increased either by lengthening the times of mixing or relaxation of the dough. The incorporated [35S] cysteine could be released in dough only by the addition of large excess of unlabelled cysteine.

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