Blocked N-terminus

[Shaun D. Black]

Dear Mark et al.,
     Blocked N-termini of proteins are a pain in the neck, but not so bad 
as they used to be.  The known ways an N-terminus can become covalently 
blocked are:

	1. Acetylation (from acyltransferase or via Serine O-N shift)
        2. Formylation (relatively rare)
	3. Pyroglutamylation (cyclization of an N-terminal Gln residue)
	4. Cyclization of N- and C-termini (only in some small peptides)
	5. Myristoylation (in certain membranous proteins)

Any of these can be determined if the N-terminal peptide is examined by 
mass spectral analysis.  The blocking group can be reversed in the cases of 
#1, #2, and #3, by, for example, acylase (for #1) or pyroglutamte amino 
peptideas (#3).  (These enzymes can be purchased from Takara Biomedicals
[800-544-9899] as one example).  I'm not aware of any way to deal with #4
or #5 other than isolation and MS analysis.  Hope this helps.  -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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