I tried this procedure on sperm whale myoglobin before Mark Hermodson
published the method. To our delight the reagent cleaved after all the
tryptophan residues in high yield, but it also cleaved after one tyrosine.
It is an easy method to use, yields are generally high, but beware of
an occasional non-specific cleavage.
We found that a 1-chlorobutane extraction step removes excess BNPS-skatole
from aqueous solutions. A good last step clean-up when using the
BNPS-skatole procedure.
-Lowell H. Ericsson, Dept. of Biochemistry, U. of Washington, Seattle, WA