2015
CH908, Homework #4.
1: You ran an in-gel digest experiment using Trypsin as your cleavage enzyme and
found peaks in the mass spectrum corresponding to the masses below.
i. What is an in-gel digest experiment?
ii. How can the peaks from an in-gel digest experiment be used to assign a
protein identity to a gel-band?
iii. What protein is this?
iv. Can you determine if it has any post-translational modifications, or if the
termini are modified somehow?
802.50
903.56
1064.44
1192.54
1571.87
1658.78
1963.03
2275.25
1493.23
1550.38
2647.20
2. In the mass spec image shown below, the authors assign m/z 283.2632 to an 18:1
fatty acid. (http://onlinelibrary.wiley.com/doi/10.1002/jms.3216/pdf)
i. Are they correct in their assignment?
ii. What is the ion suppression effect in mass spectrometry ionization?
iii. How many possible elemental compositions would be consistent with the
mass 283.2632 and 1.65 ppm mass accuracy? What about the peak at m/z
815.7099?
iv. How could they improve their confidence in their assignment?
3. In the paper linked below, the authors use MALDI-TOF mass spectrometry to
identify virus strains based on the proteins detected.
(http://www.nature.com/srep/2014/141030/srep06803/pdf/srep06803.pdf)
i. What kind of proteins are they?
ii. How can they tell if the proteins are, for example, phosphorylated?
iii. Could they quantify the number of virus particles in a cell?
iv. Could they quantify the various component proteins in the virus particle?