SUMMARY: β-Lactamases (EC. from strains of Gram-negative bacteria have been studied using analytical isoelectric focusing. This permits a visual comparison of the patterns of β-lactamase bands produced by enzymes from different organisms. Purification of crude intracellular preparations is unnecessary and the technique is sufficiently sensitive to demonstrate β-lactamase in mutants previously reported to lack the enzyme. R factor RTEM and RP1 β-lactamases that have not been distinguished from one another biochemically or immunologically can be differentiated by isoelectric focusing. Conversely, the enzymes specified by the R factors RTEM, R1 and R, with identical isoelectric focusing patterns, have the same biochemical properties. Chromosomal and R factor-mediated β-lactamases from single strains have been separated and their identities confirmed by immunoisoelectric focusing. R factor-mediated enzymes gave identical isoelectric focusing patterns irrespective of the host strain. Isoelectric focusing can therefore be used to observe the transfer of β-lactamases carried by R factors.


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