Purification and characterization of a plasmid-encoded aminoglycoside-(3)-N-acetyltransferase IV from Escherichia coli.

Plasmid-encoded aminoglycoside-(3)-N-acetyltransferase IV, AAC(3)-IV, was purified to homogeneity by affinity chromatography from E. coli. The enzyme was shown to consist of a monomer, with the apparent Mr being in agreement with that calculated from the nucleotide sequence of the aacC4 gene (Mr 28 500). Determination of the sequence of the N-terminal 6 amino acids revealed that processing did not occur, indicating the cytoplasmic localization of the AAC(3)-IV enzyme. A correlation of antibiotic resistance with Km values of the purified enzyme for a corresponding set of aminoglycoside substrates is discussed with respect to the mechanism of resistance in vivo.