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Introduction to Enzyme and Coenzyme Chemistry - E-Library Home

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Enzymatic Addition/Elimination Reactions 197<br />

H AEnz<br />

HO H O<br />

C 6 H 13<br />

SR<br />

H S H R<br />

HN N<br />

His 70<br />

C 6 H 13<br />

HN<br />

His 70<br />

HO H<br />

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H<br />

− AEnz<br />

H<br />

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SR<br />

H AEnz<br />

H S O<br />

C 6 H 13<br />

SR<br />

H R<br />

+ H 2 O<br />

HN N<br />

His 70<br />

H AEnz<br />

O<br />

C 6 H 13<br />

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His 70<br />

C 6 H 13<br />

HN<br />

His 70<br />

N<br />

H<br />

− AEnz<br />

H<br />

O<br />

SR<br />

Figure 8.6 Mechanism for b-hydroxydecanoyl thioester dehydratase.<br />

H +<br />

EnzB:<br />

H<br />

H<br />

O<br />

S<br />

NAc<br />

allene<br />

intermediate<br />

H<br />

N<br />

O<br />

H<br />

S<br />

NAc<br />

N<br />

H<br />

N<br />

O<br />

S<br />

NAc<br />

N<br />

O −<br />

S<br />

NAc<br />

N<br />

N<br />

covalently modified enzyme<br />

Figure 8.7 Irreversible inhibition of b-hydroxydecanoyl thioester dehydratase.<br />

aconitase; <strong>and</strong> the hydration of fumarate <strong>to</strong> malate catalysed by the enzyme<br />

fumarase. Both these enzymes were found at an early stage <strong>to</strong> be dependent<br />

upon iron for activity. When the enzymes were puriWed <strong>and</strong> characterised, both<br />

enzymes were found <strong>to</strong> contain [4Fe4S] iron–sulphur clusters at their active<br />

sites. The usual biological function of iron–sulphur clusters, as explained in

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