Chem167_L17_May30

To lactamases enzymes which hydrolyse the lactam ring

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Unformatted text preview: Enz-Nu -H O H S N Me Me O H CO2H C HH N H R O C HN Nu-Enz S Me Me CO2H • Covalent bond formed to transpepKdase enzyme • Irreversible inhibiKon Mechanism of acKon - bacterial cell wall synthesis NAM L- Ala D- Glu L- Lys NAG NAM L- Ala D- Glu L- Lys Bond formaKon inhibited by penicillin NAM L- Ala NAG D- Glu NAM L- Lys L- Ala D- Glu L- Lys NAG NAM NAM L- Ala NAG L- Ala NAG D- Glu L- Lys NAM D- Glu L- Ala NAM NAG L- Lys L- Ala D- Glu L- Lys NAM L- Ala D- Glu D- Glu L- Lys L- Lys Mechanism of acKon - bacterial cell wall synthesis NAM NAG NAM L-Ala L-Ala D-Glu NAG SUGAR BACKBONE D-Glu L-Lys Gly Gly Gly Gly Gly L-Lys D-Ala D-Ala D-Ala Gly Gly Gly Gly Gly D-Ala PENICILLIN D-Alanine NAM NAG TRANSPEPTIDASE NAM L-Ala L-Ala D-Glu NAG D-Glu L-Lys D-Ala Gly Gly Gly Gly Gly Cross linking L-Lys D-Ala Gly Gly Gly Gly Gly SUGAR BACKBONE Mechanism of acKon - bacterial cell wall synthesis • Penicillin inhibits final crosslinking stage of cell wall synthesis • It reacts with the transpepKdase enzyme to form an irreversible covalent bond • InhibiKon of transpepKdase leads to a weakened cell wall • Cells swell due to water entering the cell, then burst (lysis) • Penicillin possibly acts as an analogue of the L- Ala- γ- D- Glu porKon of the pentapepKde chain. However, the carboxylate group that is essenKal to penicillin acKvity is not present in this porKon Mechanism of acKon - bacterial cell wall synthesis AlternaKve theory- Pencillin mimics D- Ala- D- Ala. Normal Mechanism Peptide Chain Peptide Chain D-Ala OH Peptide Chain Peptide Chain D-Ala CO 2 H D-Ala Gly D-Ala O H OH Peptide Chain Gly Mechanism of acKon - bacterial cell wall synthesis AlternaKve theory- Pencillin mim...
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