As far as I know, disulfides are functions of secreted, extracellular proteins.
(or, of course, within the ER during sorting). However, some cytoplasmic
proteins do have disulfides, but such are not aimed at structural rigidity.
Rather, these are used in redox reactions. Two examples that I know of are
the active sites of thioredoxin and glutathione reductase. I hope this helps.
Bye for now. -Shaun
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= Shaun D. Black, PhD | Internet address: shaun at jason.uthct.edu =
= Dept. of Biochemistry | University of Texas Health Center, at Tyler =
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