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

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Abstract
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 M r being in agreement with that calculated from the nucleotide sequence of the aacC4 gene (M r 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 K m values of the purified enzyme for a corresponding set of aminoglycoside substrates is discussed with respect to the mechanism of resistance in vivo.