Question

How does the modification of specific Lys residues in a protein, for example, through the use of reagents like NHS ester, impact the equilibrium between protonated and deprotonated forms of these residues? Specifically, if some Lys residues are chemically modified, do the remaining unmodified Lys residues undergo protonation or deprotonation to counteract the effects of the modification and maintain the overall equilibrium? Additionally, is it generally impossible to achieve 100% modification of a particular Lys residue due to the existence of this equilibrium state?

Answer 1

Chemical modifications of Lys residues in proteins can impact the equilibrium between protonated and deprotonated forms. Unmodified Lys residues may undergo protonation or deprotonation to maintain overall equilibrium. It is generally impossible to achieve 100% modification of a particular Lys residue due to the equilibrium state.

Step-by-step explanation:

Chemical modifications of specific Lys (lysine) residues in a protein can impact the equilibrium between protonated and deprotonated forms of these residues. For example, the use of reagents like NHS ester can modify the Lys residues by adding a moiety to them.

This modification can lead to a change in the pKa value of the Lys residue, affecting its protonation state.

If some Lys residues are chemically modified, the remaining unmodified Lys residues may undergo protonation or deprotonation to counteract the effects of the modification and maintain the overall equilibrium. This is because the equilibrium between protonated and deprotonated forms depends on factors like the pKa of the residue and the pH of the environment.

It is generally impossible to achieve 100% modification of a particular Lys residue due to the existence of this equilibrium state. Even if a high percentage of the Lys residues are modified, there will still be a small fraction of unmodified residues that can undergo protonation or deprotonation.