Disulfide-sulfhydryl interchange reactions

Since part of the insolubilization of heated soy milk protein during drying occurs through the sulfhydryl/disulfide bond interchange reaction, experiments were carried out so as to distinguish... 

Figure 1.73 The disulfide group of a cystamine-modified protein may undergo disulfide interchange reactions with another sulfhydryl-containing protein to yield a disulfide-linked conjugate.

Figure 21.10 Cystamine may be used to make immunotoxin conjugates by a disulfide interchange reaction. Modification of antibody molecules using an EDC-mediated reaction creates a sulfhydryl-reactive derivative. A-chain toxin subunits containing a free thiol can be coupled to the cystamine-modified antibody to form disulfide crosslinks.

There is another phenomenon, regarded as a deteriorative change in the protein of soy milk, caused also by the evaporation of water. This is a film formation on the surface of soy milk, which occurs when heated soy milk is kept open to the air. This phenomenon is observed not only in heated soy milk but also in heated cow s milk. Film formation of soy milk occurs only when the soy milk is heated above 60°C and there is evaporation of water from the surface of the soy milk. The mechanism of protein insolubilization is basically the same as that of soy milk powder produced from heated soy milk (10. When water is removed from the surface of heated soy milk by evaporation, the molecular concentration of protein near the surface increases locally and the exposed reactive groups of the denatured molecules come close enough to interact intermolecularly both by hydrophobic interactions and through the sulfhydryl/disulfide interchange reaction to form a polymerization (film) on the surface. The upper side of the film contains more hydrophobic amino acids because of orientation of the hydrophobic portions of the unfolded molecules to the atmosphere rather than into the aqueous solution. 

Figure 7. Increase in the insolubilization of soybean protein during frozen storage at —5°C by the addition of small amounts of mercaptoethanol (ME), indicating the promotion of a sulfhydryl/disulfide interchange reaction by a disulfide bond splitting agent (lOj...

This enzyme [EC 5.3.4.1], also known as S—S rearran-gase, catalyzes the rearrangement of intrachain or interchain disulfide bonds within proteins to form then-native structures. The enzyme requires reducing agents or the partly reduced enzyme. The reaction operates by sulfhydryl-disulfide interchange. 

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