Electrospray ionization mass spectrometry (ESI-MS) of proteins involves creating

Question

Electrospray ionization mass spectrometry (ESI-MS) of proteins involves creating positively charged ions of the protein and separation of them according to their mass-to-charge ratio (m/z)

Electrospray ionization mass spectrometry (ESI-MS) of proteins involves creating positively charged ions of the protein and separation of them according to their mass-to-charge ratio (m/z) (3 points) a. What causes the different positive charges on different particles of the protein? b. The amino acid composition (in numbers of residues per chain) of hen egg-white lysozyme (HEWL) is as follows. P 2 D 7 C 8 A 12 S 10 Y 3 M 2 R 11 I 6 W 6 N 14 8 G 12 K 6 T 1 H 1 E 2 F 3 Q3 What is the maximum positive charge that can be present on HEWL peptide ion?

Explanation / Answer

(a) The positive charges are caused by the protonation of basic side chains (H, K, and R) and the N-terminal amino groups of the protein.

(b) There is 1 H, 6 K, 11 R, and 1 NH2 at the N-terminus. Therefore, the maximum number of  positive charges that can be obtained is 19.

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