The carbanion of nitroethane is an inhibitor of, and not a substrate for, flavocytochrome b2 [L-(+)-lactate dehydrogenase].

Although nitroethane does not bind to the active site of flavocytochrome b2, its anion, ethane nitronate, behaves as a competitive inhibitor, with a Ki of 2.2 mM. No electron transfer can be detected between the nitronate and the enzyme, in contrast with the observations of other workers on D-amino acid oxidase. Propionate is a competitive inhibitor, with a Ki of 28 mM. The significance of these results with respect to the proposed carbanion mechanism and the putative existence of a covalent enzyme-substrate intermediate is discussed.