Final answer:
The oxidation step in ethanol metabolism, which involves the conversion of ethanol to acetaldehyde, exhibits zero-order kinetics and is catalyzed by alcohol dehydrogenase.
Step-by-step explanation:
The step in ethanol (ETOH) metabolism that operates under zero-order kinetics is oxidation. This means that at high concentrations of ethanol, the rate of metabolism is constant and does not increase with higher ethanol levels. The enzyme responsible for this process, alcohol dehydrogenase, catalyzes the oxidation of ethanol to acetaldehyde. When the ethanol concentration is high, the enzyme is saturated, and the reaction proceeds at a maximal rate that does not change with additional substrate (ethanol). This characteristic is indicative of zero-order kinetics where the reaction rate is independent of the substrate concentration.