Introduction to Enzyme and Coenzyme Chemistry - E-Library Home

152 Chapter 6
CoA. Explain these results, and write a mechanism for the enzymatic
reaction.
(3) The enzyme which catalyses the conversion below has been puriWed
and requires a catalytic amount of NAD þ for activity. Given that H
is transferred intact as shown, suggest a mechanism for the enzymatic
reaction.
HO
*H
*H
HO
OH
O
OCDP
OH
ENZ
cat. NAD +
O
OH
O
OCDP
OH
(4) The reductase enzyme which catalyses the reaction shown below contains a
stoichiometric amount of tightly bound FAD, which is reducible during
catalytic turnover, and utilises NADPH as a reducing equivalent. Incubation
of 4S- 2 H-NADPD with enzyme and substrate gives product containing
one atom of deuterium b to the carboxylate. Incubation with unlabelled
NADPH in 2 H 2 O gives product containing one atom of deuterium a to the
carboxylate. Suggest a mechanism for the enzymatic reaction consistent
with these data.
OH
OH
HO
O
O
ENZ
FAD
HO
O
O
CO 2
−
AcNH OUDP
NADPH NADP +
H β
H α
CO 2
−
AcNH OUDP
(5) A Xavo-enzyme has been puriWed which catalyses the conversion of
para-nitrophenol into hydroquinone and nitrite. The enzyme contains
tightly bound FAD, and each catalytic cycle consumes one equivalent of
dioxygen and two equivalents of NADH. Suggest a mechanism.
NO 2
OH
OH
ENZ
FAD, O 2 ,
2 x NADH
OH
+ NO 2
−