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You need this problem to solve the next question below.. DONT NEED TO ANSWER THIS PROBLEM BUT PLEASE HELPE ME WITH THE NEXT PROBLEM UNDER.

You use the information above to solve this problem [which is the one I need help on] SO MAY SOMEONE HELP ME ON THIS PROBLEM PLEASE?

Assume that the amino acids with ionizable side chains have the following pKas Asp, 3.65; Glu, 4.25; His, 6.00; Lys, 10.53, Arg, 12.48; Cys, 8.18; Tyr, 10.07 Also, assume that the -amino group has a pKa of 9.60, and the -carboxyl group has a pKa of 2.30 What would be the approximate pI value of the following protein (note that it is a hemoglobin, though that doesn't matter)-? (Be sure to write out your logic!) Amino Acid Moles/Mole Protein His Ar 4 Asn 10 4 Ser Glu Gln Gl Ala 20 28 10 Val Met Ile Leu Phe

Explanation / Answer

Lets separate the charged residues out.

from Table 1. (I write the no. of amino acids of charged residues)

Positively(+ve) charged: LYS: 11 ; ARG: 3 , total positive charge = 11+3 = 14

Negatively (-ve) charged: ASP: 8; GLU : 4 , total negative charge= 8+4 = 12

Net charge on the protein1 (let me call this as protein 1) : +2 (positive)

From Table 2.

+ve: LYS+ARG = 13+5 = 18

-ve: ASP+GLU = 10+6 = 16

Net charge on the protein2: +2 (positive) . Since both are having same net charge(+2) it cannot me separated by charge.

Length of protein1 (total no. of amino acid) : 147

Length of protein2 (total no. of amino acid) : 147

The trick is going to be then the no. of HIS. In protein1 it is 6 and in protein2 it is 2. At lower pH (pH < 6.0, say 5.0 ) the His will be postively charge . Since protein1 has more His, it will have more positive charge and can be seperated using isoelectric point precipitation.

https://en.wikipedia.org/wiki/Protein_precipitation#Isoelectric_point_precipitation

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