Which of the following is a recognized class of enzymes?

• A. Oxidoreductase
• B. Kinase
• C. Synthetase
• D. Protease

Answer: (A)

Enzyme classification is organized by the type of chemical transformation they catalyze, with a standard set of broad families. Oxidoreductases are those that catalyze oxidation-reduction reactions, transferring electrons between molecules and often using cofactors such as NAD+/NADP+ or FAD. This makes oxidoreductases a recognized major class in the enzyme classification system. Kinases are enzymes that transfer phosphate groups and fall under transferases; synthetases (a type of ligase) join molecules using energy; proteases are hydrolases that cleave peptide bonds. So the best answer is oxidoreductase because it represents one of the fundamental, widely recognized enzyme classes.