Introduction to Enzyme and Coenzyme Chemistry - E-Library Home

250 Chapter 11
O
HN
NH
+
H 3 N
H 3 C
+
S
CO 2
−
HO
O
OH
Ad
S-adenosyl Met
9
6
H C
H 2
[4Fe4S] red [4Fe4S] ox
H 2 C Ad
O
L-Met
HO
OH
O
CO 2 H
H 3 C
O
Ad
HN
NH
O
O
9
HO OH H 2 C
O
AdoMet HN
AdoMet H 2 C
CH 3
S
NH
6
[4Fe4S]
CO 2 H
CO 2 H
HN
H
S
NH
H
H
CO 2 H
HN
H 2 C
S
NH
6
CO 2 H
[FeS]
[FeS]
Figure 11.15 Mechanism for biotin synthase.
that the enzyme eVectively self-destructs in order to complete one catalytic
cycle, which is one of several remarkable features of this enzyme.
Sulphur insertion reactions have also appeared in the biosynthesis of coenzymes
thiamine and molybdopterin, and in the modiWed RNA base thio-uridine.
This area of enzymology is therefore expanding rapidly at present, and the
emergence of X-ray crystal structures of these enzymes is eagerly awaited.
11.6 Oxidised amino acid cofactors and quinoproteins
At the same time that protein radicals were being discovered in enzyme active
sites, several unusual amino acid cofactors were being studied. In the active site
of galactose oxidase from Fusarium spp., a copper metallo-enzyme, a modiWed