Enzyme Class for Oxygenase-Catalyzed PAH Degradation

The question asks to identify the enzyme class responsible for the initial step in the degradation of polycyclic aromatic hydrocarbons (PAHs) using molecular oxygen. Enzymes that perform this function are known as oxygenases.

Understanding Oxygenase Function

• Oxygenases incorporate oxygen atoms into organic substrates.
• The process typically involves an oxidation reaction, where the substrate is oxidized, and molecular oxygen (O₂) acts as an oxidant.
• Specifically, the initial step in PAH degradation often involves monooxygenases or dioxygenases, which are types of oxygenases.

Matching Function to Enzyme Class

The standard classification of enzymes (EC numbers) categorizes enzymes based on the type of reaction they catalyze:

• Oxido-reductases (EC 1): Catalyze oxidation-reduction reactions. This includes enzymes that use molecular oxygen as an oxidant or incorporate oxygen atoms into substrates.
• Hydrolases (EC 3): Catalyze the cleavage of bonds using water.
• Transferases (EC 2): Catalyze the transfer of a functional group from one molecule to another.
• Lyases (EC 4): Catalyze the cleavage of bonds by elimination, forming double bonds or rings, or conversely, addition across double bonds.

Since oxygenases utilize molecular oxygen and facilitate an oxidation process during PAH degradation, they fall under the Oxido-reductase class.

Conclusion

The enzymes catalyzing the initial oxidative step in PAH degradation using molecular oxygen are classified as Oxido-reductases.