which of the foloowing polypeptides with single letter abbre

which of the foloowing polypeptides (with single letter abbreviations for the residues) will bind the strongest( elute last) at ph 7 from an ion excahnge column packed with a matrix (stationary phase) having only negative charges on the surface?

1. TDLSWQEM

2. PFGQAVCI

3. FKLMNKRP

THE ANSWER IN NUMBER 3 BUT I DONT KNOW HOW ARE WHY??

Solution

Lysine (Lys, K), Histidine (His, H) and Arginine (Arg, R) are the positively charged amino acid whereas Aspartate (Asp, D) and Glutamate (Glu E) are the negatively charged amino acids. According to given situation, Colom matrix surface are negatively charged which attract more positive charged amino acid and repel negative charged amino acid. “FKLMNKRP” sequence contains 2 positive charged amino acid and no negative amino acid which make this more favourable to attract negative charge. “TDLSWQEM” sequence contain no positive charged amino acid and one negative amino acid which favers only repulsion towards negative charge surface. “PFGQAVCI” sequence contain no positive or negative charged amino acid. So by this information one can predict which peptides elute first and which one will be last.