Mass spectrometry is often used for sequence analysis of peptides from 2 to 20 a
ID: 53300 • Letter: M
Question
Mass spectrometry is often used for sequence analysis of peptides from 2 to 20 amino acids in length. The procedure requires only microgram quantities of protein and is very sensitive; cationic fragments are identified by their charge-to-mass ratio. For the following peptide sequence, answer the following questions. Peptides are treated with triethylamine and then with acetic anhydride. Describe what this treatment will do to the amino groups The modified peptide is then incubated with a strong base and then with methyl iodide. Explain the effect of the strong base on the peptide and identify which groups on the peptide will be methylated at the conclusion of these treatments Which two amino acids cannot be distinguished by mass spectrometry? Explain your answerExplanation / Answer
## Although I feel that this question should be in chemistry; still as far as my knowledge is concerned I will give it a try. Exact reaction can be given only if posted as chemistry question.
a) Tri ethyl amine and acetic anhydride removes the amine group (-NH2) from the amino acid acid on which it is acting on; and replaces it NH- C=O. In other words it reduces the amine group.
b) Strong base will finally convert C=O into CO Na (means further reduction will occur). Finally this Na is replaced by CH3 of methyl iodide.
Arg and Lys having free amino groups should be methylated after the above reactions.
c) The amino acids which have no difference in their masses like Iso and Leu or which differ in masses by a very nominal ratio; like Glu and Lys (128 Da) Phe and oxidised Met (147Da) cannot be distinguished by mass spectrometry.