Question

3. Which class defines the following enzyme: Aconitase?

A. Lyase

B. Oxidoreductase

C. Hydrolase

D. Ligase

E. Transferase

I'm stuck between whether it's lyase and hydrolase.

4. Which class defines the following enzyme: Lipoxygenase?

A. Lyase

B. Oxidoreductase

C. Hydrolase

D. Ligase

E. Transferase

Answer 1

3. Answer:   Lyase

Hydrolase catalyzes the hydrolysis of a chemical bond. Means addition of H₂O, but aconitase dehydrates removes H₂O. Dehydratases are a group of lyase enzymes that form double and triple bonds in a substrate through the removal of water. Hence aconitase belongs to lyase. See citric acid cycle also.

4. Answer:      Ligase

Lipoxygenase catalyze the incorporation of molecular oxygen like ligase, ligase enzyme catalyzes the linking together of two compounds, e.g., enzymes that catalyze joining of C-O, C-S, C-N, etc.i.e the joining of two large molecules by forming a new chemical bond.

Addition of O2 to Arachidonate by lipoxygenase enzyme gives 12-Hydroperoxyeicosatetraenoate (12-HPETE), here a new C-O bond formed as C-H becomes C-O-O-H means new C-O bond formation.

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