The first step in polyethylene glycol degradation by sphingomonads proceeds via a flavoprotein alcohol dehydrogenase containing flavin adenine dinucleotide

Several Sphingomonas spp. utilize polyethylene glycols (PEGs) as a sole car bon and energy source, oxidative PEG degradation being initiated by a dye-l inked dehydrogenase (PEG-DH) that oxidizes the terminal alcohol groups of t he polymer chain. Purification and characterization of PEG-DH from Sphingom onas terrae revealed that the enzyme is membrane bound. The gene encoding t his enzyme (pegA) was cloned, sequenced, and expressed in Escherichia coli. The purified recombinant enzyme was vulnerable to aggregation and inactiva tion, but this could be prevented by addition of detergent. It is as a homo dimeric protein with a subunit molecular mass of 58.8 kDa, each subunit con taining 1 noncovalently bound flavin adenine dinucleotide but not Fe or Zu. PEG-DH recognizes a broad variety of primary aliphatic and aromatic alcoho ls as substrates. Comparison with known sequences revealed that PEG-DH belo ngs to the group of glucose-methanol-choline (GMC) flavoprotein oxidoreduct ases and that it is a novel type of flavoprotein alcohol dehydrogenase rela ted (percent identical amino acids) to other, so far uncharacterized bacter ial, membrane-bound, dye-linked dehydrogenases: alcohol dehydrogenase from Pseudomonas oleovorans (46%); choline dehydrogenase from E. coli (40%); L-s orbose dehydrogenase from Gluconobacter oxydans (38%); and 4-nitrobenzyl al cohol dehydrogenase from a Pseudomonas species (35%).