Why is kininogen binding less sensitive to pH changes?

[Mr_Bio]

Homework Statement

Why is the binding of kininogen less sensitive to physiological pH changes?

A) the pKa of the lysine side chain is much higher than that of HIS so it remains positive at higher pH
B) Lysine forms a covalent interaction with heparin
C) The lysine side chain is positively charged over the ppH range 0-14.
D) the pKa of the lysine side chain is much lower than that of HIS so it remains positive at higher pH

Homework Equations

The Attempt at a Solution

I'm stuck on this question -- I believe the answer is A) as I looked up the pkAs and this seems to be true. However, I'm not sure if there is a better answer or not.

 

[Bee529]

It's funny that I started to read this as 4 full reasons why, and I had a revelation at answer A, so I didn't even read the others. Yes, it's A. And I'm assuming that you don't need this answer anymore (or your homework is 7 years late-- edit: to the day!), but hopefully this helps others.