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Biochemistry
9th Edition
ISBN: 9781319114671
Author: Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher: W. H. Freeman
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Question

Transcribed Image Text:b.
The C-2 atom in 2-phosphoglycerate is not acidic in solution, i.e. it does not have a tendency to lose
its proton (colored blue above). However, in the active site of enolase, C-2 has a lowered pKa and is acidic
enough that Lys45 can extract its proton. Which feature of the enzyme active site do you expect to increase
the acidity of C-2?
(Hint: The transfer of the double bond on to the C-2 atom is directly linked to and stabilized by the ability of
the carboxyl group of 2-PG to become -2 charged.)
C.
Using acid-base catalysis terminology, state the roles for Glu211 and Lys345 in step 1. In other words,
what do the two side chains serve as?
To fulfill their roles, do you expect Glu211 and Lys345 to have modified pka's as compared to those of
free Glu and Lys side chains? If so, do you expect elevated or decreased pKa's for these residues within
d.
the context of the active site of enolase?

Transcribed Image Text:3.
The enzyme enolase catalyzes the removal of one water molecule ("dehydration") of 2-
Phosphoglycerate (2-PGA).
The numbering
scheme of the
enolase
carbons is labeled
HC-0-P-O
+ H20
on 2-PGA.
||
CH2
HO-CH2
2-Phosphoglycerate
Phosphoenolpyruvate
Part of the catalytic mechanism is as follows:
Mg2+
PO?-
Mg?+
PO?
'o.
Ó H
Mg?+
Mg²+;
PO?
:-C-H
C=C-C-H
OH
OH
Нон
Enolase
но
но
H-N*-H
Lys345
Lys345
Glu211
Glu211
2-Phosphoglycerate bound to enzyme
Enolate intermediate
Phosphoenolpyruvate
а.
Draw the mechanism of the reaction by adding arrows to show how electrons move.
Mg2+
PO?-
Mg2+
po
PO
H
H
Mg2+
С -с-с-н
Mg2+
C=c-C-H
H
OH
OH
Enolase
H.
H-N-H
но
но
..
H-N-H
Lys345
Lys345
Glu211
Glu211
2-Phosphoglycerate bound to enzyme
Enolate intermediate
Mg?+
PO
O.
он
Mg2+:
PO?
c=C-C-H
OH
HOH
H
но
C=C
H-N*-H
Lys345
Glu211
Enolate intermediate
Phosphoenolpyruvate
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