A new fluorene catabolic pathway has recently been
found in which hydroxylation at C-9 of fluorene generates
9-fluorenol, which is then dehydrogenated to
9-fluorenone [lo]. This intermediate then undergoes
dioxygenation at an angular site to form l,lO-dihydro-l,lOdihydroxyfluorene-
9-one (DDF), the five-membered ring
of which is subsequently cleaved to generate a substituted
biphenyl. The ring-cleavage enzyme was a purified
and characterized NAD+-dependent DDF dehydrogenase
(NAD, nicotinamide adenine dinucleotide).