Pentalenolactone synthase (, Formerly , penM (gene), pntM (gene)) is an enzyme with systematic name pentalenolactone-F:oxidized-ferredoxin oxidoreductase (pentalenolactone forming). It catalyses the rearrangement reaction
This is heme-thiolate protein (P-450), which is isolated from the bacteria Streptomyces exfoliatus and Streptomyces arenae.The transformation is the final step in the biosynthesis of pentalenolactone.