Words similar to penicillins
Example sentences for: penicillins
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When penicillins were used as substrates, the Tyr228 mutants exhibited 3- to 13-fold increased K m values and < 2-fold changes in k cat , as compared to the values ascertained using wild-type L1 (Table 4).
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.
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).
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.
On the other hand, the K m and k cat values for the I164A mutant when the penicillins or carbapenems were used as substrates were very similar to those numbers exhibited by wild-type L1 (Tables 4and 5).
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