Question

The researchers discover that the lysine residues can have their pKa values altered by changing a variety of factors in the solution. They propose several experiments, listed below. Predict the effect of the proposed changes on the pKa of the N’-PACKERS-C’ lysine side chain. Answer each part with your prediction of whether the pKa of the lysine will D (decrease), I (increase), or N (little or no change).

a)The Lys side chain is shifted to the nonpolar interior location of a binding protein.

b) The C-terminus of the peptide at pH 7.5 is brought into close proximity.

c) The solution [Na+] and [Cl-] are increased from 0.05 M to 0.10 M.

d) The N’-VIKINGS-C’ protonated lysine side chain is brought into close proximity.

Answer 1

a. Answer: Decrease shifts in pKa values of LYS  to the non polar interior location of a binding protein because Lysine is positively charged, it is polar and it is hydrophilic.

b. Answer: Increase proximity at the pH 7.5 lysine has a net charge of very close to +1 because,The carboxylic acid group is de-protonated (-1 charge) fully. The alpha amino group is having 99% protonated (+1 charge).

c. Answer: Decrease pka value because LYS are increased with solution [Na+] & [Cl-] from 0.2M to 0.2M

d. Answer:Increase becuse carboxylic acid group is de-protonated (-1 charge) fully. The alpha amino group is having 99% protonated (+1 charge).

thank you..