I have a question regarding the correct mass of several proteins and
peptides that I have been using for calibration standards.
One of the standards I have been using is Bovine Insulin oxidized beta
chain. Sigma lists the mass as 3495.9 Bruker's calibration list also lists
the monoisotopic mass as 3494.65. But when I pull the amino acid sequence
from swiss-prot and Do the calculations on both Rockefellers web site and
EMBL's web site, I get a monoisotopic mass of 3397.674. What could account
for this mass difference? Am I doing something wrong?
The other standard is Horse heart cytochrome C. Sigma lists the mass as
12384, Bruker lists the average mass as 12361.088 and I get an average
calculated mass of 12374.02 including 1 Fe atom and 1 heme group with a mass
of 616.6. Additionally, when I buy my standards from Sigma, for example,
What modifications are on the cytochrome C. Swis-prot says cytochrome C has
the following modifications
Post translational modification: 1 ACETYLATION
Binding site: 14 HEME (Covalent)
Binding site: 17 HEME (Covalent)
Binding site for metal ion: 18 IRON (Heme axial ligand)
Binding site for metal ion: 80 IRON (Heme axial ligand)
But the average mass with all of these modifications (calculated from
Rockefeller's web site (www.proteimetrics.com)is 13088.50.
Which mass is correct? and what am I actually getting from sigma?
Thanks a lot in advance for the help
__________________________________
Brett Phinney
North Carolina State University
Department of Biochemistry
Ph# 919-515-5786, Fax 919-515-2047
ICQ# = 12442943