MOLECULAR CHARACTERIZATION OF PADA, A PHENYLACETALDEHYDE DEHYDROGENASE FROM ESCHERICHIA-COLI

The padA gene encoding the phenylacetaldehyde dehydrogenase involved i n the catabolism of 2-phenylethlamine in Escherichia coli has been clo ned, sequenced, and located at 31.0 min on the chromosome. The deduced PadA polypeptide contains 499 amino acid residues with a predicted mo lecular mass of 53.7 kDa, and its primary structure reveals significan t similarity with that of members of the aldehyde dehydrogenase superf amily. By engineering optimal transcription and translation elements, a high expression of the padA gene has been achieved. The active PadA enzyme is a homodimer that prefers NAD(+) over NADP(+) as coenzyme. Th e enzyme efficiently oxidizes only phenylacetaldehyde-like aromatic al dehydes, and has a weak esterase activity with p-nitrophenol. The padA gene constitutes a new catabolic tool for designing DNA cassettes to expand the abilities of microorganisms to degrade toxic aromatic compo unds. (C) 1997 Federation of European Biochemical Societies.