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Oxigenases/deoxygenases containing the molybdopterin cofactor, Fig. 19.
O O
VI
Mo
O O H S X
N N S
HN HN
O O
H N N N H N N N O O P O P O Cyt/Gua
2
2
H
Pterin O OH
Molybdopterin

O O O

Mo VI + Substrat Mo IV + Substrat-O
S X S X
S S

Figure 19. Oxidised form of the molybdopterin cofactor (upper right) of the sulphite reductase
-
family. X usually is Cys . Molybdopterin transfers oxido groups to a substrate (shown) or off a
substrate.

An example is the (dissimilatory) nitrate reductase:
-
+
-
-
NO 3 + 2e + 2H → NO 2 + H 2O)
O O O O
IV VI
Mo + NO3 Mo N O NO2 + Mo O
O
+ FADH2

Vanadate-dependent haloperoxidases from marine algae catalyse the oxidation of halide
+
+
-
(Hal ) to a Hal species such as hypohalous acid. Oxidant is hydrogen peroxide. The Hal
species halogenates organic substrates non-enzymatically. For the mechanism, see Fig. 20.

+
-
Hal + H 2O 2 + H → HalOH + H 2O
HalOH + RH → RHal + H 2O

NH +
H +
N OH H Br -
H 2 O O + H 2 O 2 O O O O
H H 2 O V V V
O O O H
OH H 2 O
O V HO CH 2
O
N CH
HOBr
NH

Figure 20. Active centre of vanadate-dependent haloperoxidase (left), and mechanism of the
enzymatic formation of hypobromous acid from bromide (right).