This enzyme participates in the biosynthetic pathway for UDP-¦Á-D-ManNAc3NAcA (UDP-2,3-diacetamido-2,3-dideoxy-¦Á-D-mannuronic acid), an important precursor of the B-band lipopolysaccharide of?Pseudomonas aeroginosa?serotype O5 and of the band-A trisaccharide of?Bordetella pertussis, both important respiratory pathogens [1]. The enzyme is highly specific as UDP-¦Á-D-GlcNAc, UDP-¦Á-D-GlcNAcA (UDP-2-acetamido-2-deoxy-¦Á-D-glucuronic acid) and UDP-¦Á-D-GlcNAc3NAc (UDP-2,3-diacetamido-2,3-dideoxy-¦Á-D-glucose) cannot act as substrates [1].