Question

Why isoelectric point of arginine is greater than lysine?

Answer 1

Thanks for the question!

It is definitely a very interesting question to solve and do some brainstorming.

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The isoelectric point or the pI is the specific molecular carrier which has no net or total charge or in electrical means is completely neutral through a arithmetical or statistical mean. The three pKa values, that is, pKa1 (alpha-carboxyl group), pKa2 (alpha-ammonium ion), pKa3 (alpha phase side chain group) of Arginine are 2.17, 9.04 and 12.48 respectively. The three pKa values of lysine are 2.18, 8.95 and 10.53 respectively.
Arginine has a isoelectric point or pI of 10.76 when compared to lysine it has a lower value of isoelectric point or pI, that is, 9.74, so, by this means the isoelectric point of Arginine is greater than lysine. Since, every provided essential and non-essential amino acid has a different isoelectric point, Arginine has a higher isoelectric point due to the delocalisation of the positive charges within the pie- bonded system on the side chain of guanidinium ion, so, this becomes more stable at the Arginine side chain transferring a proton hen they have been partially buried within a protein structure or membrane, that is, lysine and Arginine began to lose their positive charges at early stages and change their pH drastically, but, lysine is more concentrated on the ending or last created aliphatic amino group and the transferring of protons through interactions of aliphatic parts or C-Beta and C-epsilon of lysine chain, making Arginine higher than lysine in all aspects, as, the angles too are on different levels.

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Hope it helps and solves your query!!