Question 24.1: Analyze the following reaction by considering the functional...
Analyze the following reaction by considering the functional groups that change and the name of the enzyme.
Analysis
• Consider the functional groups that are added or removed as a clue to the type of reaction.
• Classify the reagent (when one is given) as to the type of reaction it undergoes.
• Use the name of the enzyme as a clue to the reaction type.
The -\mathrm{COO}^{-} of pyruvate is lost as \mathrm{CO}_2 , meaning that a decarboxylation has occurred. This is supported by the type of enzyme, a decarboxylase, which typically catalyzes decarboxylations (Table 21.3). A carbon–carbon bond is broken in the process, giving \mathrm{CO}_2 as one of the products. No coenzyme is used here; the reaction does not involve oxidation, reduction, or thioester synthesis.
| Table 21.3 Classification of Enzymes | |
| Enzyme Class or Subclass | Reaction Catalyzed |
| Oxidoreductases | Oxidation–reduction |
| • Oxidases | • Oxidation |
| • Reductases | • Reduction |
| • Dehydrogenases | • Addition or removal of 2 H’s |
| Transferases | Transfer of a group |
| • Transaminases | • Transfer of an \mathrm{NH}_2 group |
| • Kinases | • Transfer of a phosphate |
| Hydrolases | Hydrolysis |
| • Lipases | • Hydrolysis of lipid esters |
| • Proteases | • Hydrolysis of amide bonds in proteins |
| • Nucleases | • Hydrolysis of nucleic acids |
| Isomerases | Isomerization |
| Lyases | Addition to a double bond or elimination to give a double bond |
| • Dehydrases | • Removal of \mathrm{H}_2 \mathrm{O} |
| • Decarboxylases | • Removal of \mathrm{CO}_2 |
| • Synthases | • Addition of a small molecule to a double bond |
| Ligases | Bond formation accompanied by ATP hydrolysis |
| • Carboxylases | • Bond formation between a substrate and \mathrm{CO}_2 |