Overexpression and initial characterization of the chromosomal aminoglycoside 3'-O-phosphotransferase APH(3')-IIb from Pseudomonas aeruginosa.

The chromosomal gene aph(3')-IIb, encoding an aminoglycoside 3'-phosphotransferase in Pseudomonas aeruginosa, was cloned and overexpressed in Escherichia coli. The APH(3')-IIb enzyme was purified as a monomer in a two-step procedure and was shown to phosphorylate its substrates at the C-3'-OH position, with kcat/Km values of 0.4x10(4) to 36x10(4) M-1 s-1.