The Mo enzyme pyrogallol-phloroglucinol transhydroxylase (TH) from the anaerobic microorganism Pelobacter acidigallici catalyses the conversion of pyrogallol to phloroglucinol. Such trihydroxybenzenes and their derivatives represent important building blocks of plant polymers.

The overall reaction appears as transfer of the 2-hydroxy group of 1,2,3,5-tetrahydroxybenzene to the C5 position of pyrogallol (systematic name 1,2,3-trihydroxybenzene). This converts pyrogallol into 1,2,3,5-tetrahydroxybenzene, and 1,2,3,5-tetrahydroxybenzene into phloroglucinol (systematic name 1,3,5-trihydroxybenzene). Therefore, the net reaction consumes no 1,2,3,5-tetrahydroxybenzene.

TH is cytoplasmic and consists of a large alpha subunit and a small beta subunit. The beta subunit contains several Fe-S clusters, which have no known function and may be evolutionary relics. This subunit also has a fibronectin-like domain which can be used for membrane association. The alpha subunit contain the Mo-binding site (with Mo coordinated to two molybdopterin guanine dinucleotide (MGD) cofactors) and the catalytic active site. Like other members of the DMSO-reducing enzyme family, Mo cycles between +4 and +6 oxidation states for catalytic activity.