[element41skater]

What is the net charge of your pentapeptide at physiological pH 7.4 and pH 1.5?


This is my pentapeptide: ala-leu-glu-hos-his.


N-terminus has a pk~9
glu has a pk~4
his has a pk~6
c-terminus has a pk~3


How do i determine what the charges are for each amino acid, so that i can determine my net Charge?




Thank you
Alex

[RTG]

You have to account for the exposed N & C terminus of the peptide and also all relevent side chains. Some amino acids have side chains that are either acidic or basic. For example Histidine (your C terminus) has a imidazole functional group. This functional group has a pKa of about 6. At a pH below 6 this functional group is protonated and will carry a positive charge. At a pH above 6 the functional group will be neutral and carry no charge. This is an example of an amino acid with a basic side chain. Do the same analysis for all amino acids and you should come up with your net charge.