One other thing that can happen in CNBr cleavages is cleavage of
acid labile bonds since it is done in concentrated acid. These usually
involve aspartic acid (either side) especially Asp-Pro.
Greg
Ulf,
Thanks for your comments....indeed, we did find cleavage in high
yield at a Trp-Met bond after cyanogen bromide cleavage of a
peroxide-oxidized protein. We'd done the cleavage to verify complete
oxidation and, till your message, we were baffled by this finding. Looking
hard, we found traces of cleavage at some other Trps linked to residues
other than methoinine. But we hadn't added iodide or other halides so we
wouldn't expect those to go to any great degree.
From the responses, it doesn't seem like there are examples of CNBr
cleavage at any other residue, however.
Henry Keutmann.
Gregory A. Grant
ggrant@molecool.wustl.edu