Interaction of Nocardicin A with the Penicillin‐Binding Proteins of Escherichia coli in Intact Cells and in Purified Cell Envelopes

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Abstract
This study deals with the interaction of nocardicin A with Escherichia coli penicillin‐binding proteins. Competition experiments with two different isotopically labelled β‐lactams indicated that nocardicin A interacts with penicillin‐binding proteins 1a, 1b, 2 and 4 in intact cells. Binding of nocardicin A to the penicillin‐binding proteins was abolished, or greatly reduced, when the assays were carried out with purified cell envelopes. Important differences between the binding patterns of benzyl [14C]penicillin to intact cells and to purified cell envelopes were also observed. These results suggest that the interaction of β‐lactam antibiotics with their target proteins depends to a very great extent on the state of the cell envelope as a whole.