Enzymatic Inactivation of Streptomycin by R Factor-resistant Escherichia coli

Abstract

WE have confirmed the findings of Okamoto and Suzuki¹ that a cell harbouring an R factor which carries streptomycin resistance can inactivate the drug by an enzymatic process. The inactivation can be detected either by a microbiological assay (Fig. 1), or by a biochemical assay (Table 1) following incubation of the drug with a cell-free extract of the R factor strain. The responsible enzyme, streptomycin adenylate synthetase, can be partially purified from cell-free extracts by ammonium sulphate precipitation and DEAE-‘Sephadex’ chromatography, but a more convenient source is the cell-free supernatant from exponentially growing cells submitted to osmotic shock according to the procedure of Nossal and Heppel², and a highly active enzyme preparation can be obtained in this way. The enzyme is almost completely released by a 25 min shocking of the treated cells (Table 1a). The shockate enzyme has been purified further and the properties of the purified enzyme will be published later.