The pKa values for the side chain carboxyl groups on aspartic acid and glutamic acid are usually cited as 3.9 and 4.1, respectively. Analysis of lysozyme's active site indicates that the pKa of Asp 52 is still about 3.9, but the pKa of Glu 35 is now about 6.6. Glu 35 shows a 2.5 fold increase in pKa, because:
A) the carboxyl group of Asp 52 is located in a polar environment B) the ionized carboxyl group of Asp 52 destabilizes the protonated carboxyl group of Glu 35 C) the carboxyl group of Glu 35 is located in a nonpolar environment D) the carboxyl group of Glu 35 is located in a polar environment, where it is stabilized by hydrogen bonding
The explanation says that since the pKa of the glutamic acid has increased by 2.5 times, while the pKa of the aspartic acid has not changed, which tells us that Asp 52 is in a polar environment, and that Glu 35 is in a nonpolar environment. How do we get that Glu 35 is nonpolar based on the fact that the pKa has increased to 6.6?
Then, it goes on to say that "in order to remove the dissociable hydrogen from the side chain of Glu-35, the active site must be at a pH close to a pKa of 6.6." Why does Glu-35 have a dissociable hydrogen when it is supposed to be charged? Also, I thought pH at the equivalence point is where the dissociable hydrogen comes off, not pH=pKa where there is an equal concentration of the conjugate base and conjugate acid.
Not following this explanation in the back, has anyone cracked it?
A) the carboxyl group of Asp 52 is located in a polar environment B) the ionized carboxyl group of Asp 52 destabilizes the protonated carboxyl group of Glu 35 C) the carboxyl group of Glu 35 is located in a nonpolar environment D) the carboxyl group of Glu 35 is located in a polar environment, where it is stabilized by hydrogen bonding
The explanation says that since the pKa of the glutamic acid has increased by 2.5 times, while the pKa of the aspartic acid has not changed, which tells us that Asp 52 is in a polar environment, and that Glu 35 is in a nonpolar environment. How do we get that Glu 35 is nonpolar based on the fact that the pKa has increased to 6.6?
Then, it goes on to say that "in order to remove the dissociable hydrogen from the side chain of Glu-35, the active site must be at a pH close to a pKa of 6.6." Why does Glu-35 have a dissociable hydrogen when it is supposed to be charged? Also, I thought pH at the equivalence point is where the dissociable hydrogen comes off, not pH=pKa where there is an equal concentration of the conjugate base and conjugate acid.
Not following this explanation in the back, has anyone cracked it?