Problems 1073
- Give the products of the following reaction, where T is tritium:
(Hint:Tritium is a hydrogen atom with two neutrons. Although a bond breaks four times more slowly than a bond, it
is still the first bond in the substrate that breaks.)
- Propose a mechanism for methylmalonyl-CoA mutase, the enzyme that converts methylmalonyl-CoA into succinyl-CoA.
- When transaminated, the three branched-chain amino acids (valine, leucine, and isoleucine) form compounds that have the
characteristic odor of maple syrup. An enzyme known as branched-chain acid dehydrogenase converts these compounds
into CoA esters. People who do not have this enzyme have the genetic disease known as maple syrup urine disease—so-called
because their urine smells like maple syrup.
a. Give the structures of the compounds that smell like maple syrup.
b. Give the structures of the CoA esters.
c. Branched-chain acid dehydrogenase has five coenzymes. Identify them.
d. Suggest a way to treat maple syrup urine disease.
- When UMP is dissolved in ( see Problem 27), exchange of T for H occurs at the 5-position. Propose a
mechanism for this exchange.
- Dehydratase is a pyridoxal-requiring enzyme that catalyzes an reaction. Propose a mechanism for this reaction.
- In addition to the reactions mentioned in Section 25.6, PLP can catalyze reactions. Propose a mechanism for the
following PLP-catalyzed reaction:
- PLP can catalyze both reactions (Problem 31) and reactions. Propose a mechanism for the
following PLP-catalyzed
E +
XCH 2 CH 2 CHCO PLP
−
NH 3
X−
O
CH 3 CH 2 CCO−
O
O
+ + NH 4
+
b,g-elimination:
a,b-elimination b,g-elimination
E
XCH 2 CHCO PLP
−
NH 3
X−
O
YCH 2 CHCO−
O
+
+ +NH 3
+ Y−
b-substitution
b-substitution
dehydratase
HOCH 2 CHCO PLP
−
NH 3
NH 4
O
CH 3 CCO−
O
O
+
+
+
a,b-elimination
T 2 O
ribose-5 ́-phosphate
UMP
O
O
H
HN
N
ribose-5 ́-phosphate
O
O
T
HN
N
T 2 OT=tritium;
a-keto
a-keto
C¬T C¬H
dioldehydrase
coenzyme B 12
CH 2
Co(III)
Ad CH 3 C COH
OHT
T T
+
