Introduction to Enzyme and Coenzyme Chemistry - E-Library Home

Radicals in Enzyme Catalysis 253
CH 3
+
− O 2 C
CO 2
−
benzylsuccinate
synthase
Gly
CO 2
−
− O 2 C
(4) Suggest a radical mechanism for the formation of the modiWed tyrosine
cofactor of galactose oxidase, shown in Figure 11.16, from the native
structures of Tyr-122 and Cys-228, employing the nearby copper centre.
You can assume that the copper centre can access Cu(I) and Cu(II) oxidation
states, and that air oxidation is involved.
(5) Suggest a catalytic mechanism for the quinoprotein methanol dehydrogenase
from Methylobacterium extorquens, which catalyses the oxidation of
methanol to formaldehyde, involving formation of a covalent linkage with
the pyrroloquinone (PQQ) cofactor.
HO 2 C
HN
CO 2 H
HO 2 C
HN
CO 2 H
HO 2 C
N
O
O
CH 3 OH H 2 C=O
(PQQ) ox
HO 2 C
N
OH
(PQQ) red
OH
Further reading
Vitamin B 12 -dependent enzymes
R.H. Abeles & D. Dolphin (1976) The vitamin B 12 cofactor. Acc. Chem. Res., 9, 114–20.
R. Banerjee (2003) Radical carbon skeletal rearrangements: catalysis by coenzyme
B 12 -dependent mutases. Chem. Rev., 103, 2083–94.
W. Buckel & B.T. Golding (1996) Glutamate and 2-methyleneglutarate mutase: from
microbial curiosities to paradigms for coenzyme B 12 -dependent enzymes. Chem. Soc.
Rev., 26, 329–37.
E.N.G. Marsh & C.L. Drennan (2001) Adenosylcobalamin-dependent isomerases: new
insights into structure and mechanism. Curr. Opin. Chem. Biol., 5, 499–505.
T. Toraya (2003) Radical catalysis in coenzyme B 12 -dependent isomerization (eliminating)
reactions. Chem. Rev., 103, 2095–127.