Sandbox 156: Difference between revisions
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Found in bacteria, the CAT III enzyme is responsible for conferring resistance to chloramphenicol. Chloramphenicol arrests protein synthesis by binding to the bacterial ribosomes and inhibiting [[peptidyl transferase]] activity <ref>PMID: 1544895</ref>. However, when CAT III catalyzes the acetylation of chloramphenicol, the antibiotic can no longer bind to the ribosomes and is rendered inactive. The genes for the enzyme are commonly found on the plasmid of the bacteria and have been found in a numerous bacterial species<ref>PMID: 2268277</ref>. | Found in bacteria, the CAT III enzyme is responsible for conferring resistance to chloramphenicol. Chloramphenicol arrests protein synthesis by binding to the bacterial ribosomes and inhibiting [[peptidyl transferase]] activity <ref>PMID: 1544895</ref>. However, when CAT III catalyzes the acetylation of chloramphenicol, the antibiotic can no longer bind to the ribosomes and is rendered inactive. The genes for the enzyme are commonly found on the plasmid of the bacteria and have been found in a numerous bacterial species<ref>PMID: 2268277</ref>. | ||
The enzyme consists of three identical subunits with three active sites at the subunit interfaces. The side chains of one subunit allow van der Waals contacts and two hydrogen bonds with chloramphenicol, causing binding of the substrate. The opposing subunit provides a histidine (His-195) residue essential for catalysis<ref>PMID: 8407936</ref>. Water molecules in the cavity provide a bridging hydrogen bond between the 1-hydroxyl of chloramphenicol and the hydroxyl of a threonine (Thr-174) residue. The active site of CAT III performs two acetylations of chloramphenicol and can accommodate the presence of the first | The multifunctional enzyme consists of three identical subunits with three active sites at the subunit interfaces. The side chains of one subunit allow van der Waals contacts and two hydrogen bonds with chloramphenicol, causing binding of the substrate. The opposing subunit provides a histidine (His-195) residue essential for catalysis<ref>PMID: 8407936</ref>. Water molecules in the cavity provide a bridging hydrogen bond between the 1-hydroxyl of chloramphenicol and the hydroxyl of a threonine (Thr-174) residue. The active site of CAT III performs two acetylations of chloramphenicol and can accommodate the presence of the first intermediates quite well<ref>PMID:2015231</ref>. | ||
=== Reaction of CAT III === | === Reaction of CAT III === | ||
