Question

What is the pl (isoelectric point) of the protein you chose in the previous problem? What is the pl of the peptide MEHR? You may find ExPASy's pl/MW calculation server (http://web.expasy.org/compute pi/) to be useful in calculating the pl of your protein, however, for the peptide, please calculate the pl by hand and show your work: you may use the pKa values on Wikipedia https://en.wikipedia.org/wiki/Proteinogenic amino acid# Chemical properties. you may need to copy and paste this link into your browser as ctrl-clicking it may not work) for your calculations- as always with this sort of thing, please cite which tools/tabulations you use. (5 pts)

Answer 1

Isolectric point is that where positive and negative charge are equal.

MEHR

In this peptide

Pka value of N-terminal of methionine is= 9.28

Pka value of aspartic acid (E) =4.25

Pka value of histidine (H)= 6.54

Pka value of Arginine (R) =12.3

-COOH terminal Arginien R= 1.82

There are several alogrtyms has been developed where only side chains have been taken but in some case free N-teminal and C-terminal residues also considered.

First by taking side chains only=( 4.25+6.54+12.4)/3= 7.73

Considering terminal amino and carboxylit groups

(9.28+4.25+6.54+12.3+1.82)/5=6.73

Various values of Pka is taken from: https://en.wikipedia.org/wiki/Proteinogenic_amino_acid