Protoporphyrinogen IX dehydrogenase (menaquinone) (, HemG) is an enzyme with systematic name protoporphyrinogen IX:menaquinone oxidoreductase. This enzyme catalyses the following chemical reaction
The enzyme uses three equivalents of menaquinone per molecule of protoporphyrinogen IX to provide the oxidant. It enables Escherichia coli to synthesize heme in both aerobic and anaerobic environments.