Words similar to cephalosporins
Example sentences for: cephalosporins
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When using the cephalosporins, nitrocefin, cefoxitin, and cephalothin, as substrates and the I164A mutant, there were 2- to 10-fold (only for cefoxitin) increases in K m and 2- to 4-fold increases in k cat observed (Table 3).
When the cephalosporins were used as substrates, the S224A and S224K mutants exhibited 2- to 4-fold changes in K m values (Table 3).
When cephalosporins were used as substrates, the Y228A and Y228F mutants exhibited K m values that were 6- to 45-fold higher than those observed for wild-type L1 (Table 3).
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.
On the other hand, the S224D mutant exhibited 3- to 50-fold higher K m values and 2- to 20-fold lower k cat values for the cephalosporins tested.
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