Question

The isoelectric point, pI, of the protein elastase is 8.5 , while that of lipase A is 4.9 .

What is the net charge of elastase at pH 5.1 ?
What is the net charge of lipase A at pH 2.5 ?

The isoelectric point of valine is 5.96 ; leucine , 5.98 .

During paper electrophoresis at pH 6.5 , toward which electrode does valine migrate? .
During paper electrophoresis at pH 5.5 , toward which electrode does leucine migrate?

Answer 1

The isoelectric point(pI) of the protein elastase is 8.5. At the isoelectric point(pI) the net charge on the molecule is zero. At low pH value than that isoelectric point molecule should have excess +Ve charge or excess H⁺ i.e protonated. So, the net charge will be +Ve.

The isoelectric point(pI)of the protein lipase A is 4.9. At the isoelectric point(pI) the net charge on the molecule is zero. At low pH value than that isoelectric point molecule should have excess +Ve charge or excess H⁺. So, the net charge will be +Ve.

Valine is a neutral amino acid with isoelectric point 5.96. At high pH 6.5 i.e higher than pI it will have excess -ve charge on it and it will move towards the anode.

Leucine is a neutral amino acid with isoelectric point 5.98. At low pH 5.5 i.e lesser than pI it will have excess +ve charge on it and it will move towards the cathode.