Words similar to penicillins
Example sentences for: penicillins
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Two penicillins were tested as substrates, and penicillin G and ampicillin exhibited K m values of 38 ± 12 μM and 55 ± 5 μM and k cat values of 600 ± 100 s -1and 520 ± 10 s -1, respectively (Table 4).
These bacteria become resistant by a number of mechanisms, such as producing enzymes that hydrolyze or inactivate the antibiotics, producing efflux pumps that transport the antibiotic out of the cell, or modifying their cell wall components so they no longer bind effectively to the antibiotics [ 1 2 3 ] . The most common, least expensive, and effective antibiotics are the β-lactam containing antibiotics, such as the penicillins, cephalosporins, and carbapenems [ 2 4 5 ] . These antibiotics are mechanism-based inhibitors of transpeptidase, a bacterial enzyme required for the production of a strong viable cell wall [ 6 7 ] . In response to the widespread use of β-lactam containing antibiotics, bacteria have acquired the ability to produce β-lactamases, which are enzymes that hydrolyze and inactivate β-lactam containing antibiotics.
All crystallographically characterized metallo-β-lactamases have a flexible amino acid chain that extends over the active site [ 37 42 44 45 46 47 48 49 ] . Previous NMR studies on CcrA have shown that this loop "clamps down" on substrate or inhibitor upon binding, and there is speculation that the distortion of substrate upon clamping down of the loop may drive catalysis [ 50 ] . The crystal structure of L1 showed that there is a large loop that extends over the active site, and modeling studies have predicted that two residues, Ile164 and Phe158, make significant contacts with large, hydrophobic substituents at the 2' or 6' positions on penicillins, cephalosporins, or carbapenems [ 37 ] . To test this prediction, Ile 164 and Phe158 were changed from large, hydrophobic residues to alanines to afford the I164A and F158A mutants.
A similar trend was observed in kinetic studies when using penicillins as substrates (Table 4).
Only when Ser224 was replaced with an Asp residue was there significant increases in the observed K m value for 6 of the 9 substrates tested, and the largest changes were exhibited when the penicillins were used as substrates.
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