Biochemistry: The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

Types of Reactions Catalyzed by Enzymes
ß-Cleavage and Condensation
Substitution at the Carbonyl Group (Type 5.A Reactions)

In the presence of suitable catalysts, $\beta$-keto acids can undergo Hydrolysis driven by the nucleophilic attack of a Water molecule on the carbonyl group. The enzyme oxaloacetate acetylhydrolase has been isolated from Aspergillus niger [141]:

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Thiolases have been studied in much greater detail [142, 143]. One of the primary Functions of these Enzymes is the Cleavage of $\beta$-ketoacyl-CoA derivatives, which proceeds via the displacement of a thiol group by another CoA molecule:

This reaction represents a key chain-shortening step in the $\beta$-oxidation pathway of Fatty acids, leading to their degradation (Fig. 7-1). Given that thiolases are inhibited by Reagents targeting —SH groups, it has been proposed that an active-site thiol group initially reacts with the $\beta$-carbonyl group, as depicted in equation (7-62), forming an intermediate complex. In the second step, the acyl group is subsequently transferred to CoA. Furthermore, certain thiolases are known to form Schiff bases with their substrates [143].



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