Example sentences for: penicillins

How can you use “penicillins” in a sentence? Here are some example sentences to help you improve your vocabulary:

  • 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.

  • Generally, the S224A and S224K mutants exhibited small changes in K m and k cat , while the S224D mutant yielded 20- to 40-fold increased values for K m and >10-fold decreases in k cat when using the penicillins as substrates.

  • 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.

  • There are over 300 distinct β-lactamases known, and these enzymes have been grouped by a number of classification schemes [ 8 9 10 11 12 13 14 15 ] . For example, Bush has developed a scheme, based on the enzymes' molecular properties, that has four distinct β-lactamase groups [ 10 15 ] . One of the more alarming groups are the Bush group 3 enzymes, which are Zn(II) dependent enzymes that hydrolyze nearly all known β-lactam containing antibiotics and for which there are no or very few known clinical inhibitors [ 9 14 16 17 18 19 ] . The metallo-β-lactamases have been further divided by Bush into subgroups based on amino acid sequence identity: the Ba enzymes share a >23% sequence identity, require 2 Zn(II) ions for full activity, prefer penicillins and cephalosporins as substrates, and are represented by metallo-β-lactamase CcrA from Bacteroides fragilis, the Bb enzymes share a 11% sequence identity with the Ba enzymes, require only 1 Zn(II) ion for full activity, prefer carbapenems as substrates, and are represented by the metallo-β-lactamase imiS from Aeromonas sobria, and the Bc enzymes have only 9 conserved residues with the other metallo-β-lactamases, require 2 Zn(II) ions for activity, contain a different metal binding motif than the other metallo-β-lactamases, prefer penicillins as substrates, and are represented by the metallo-β-lactamase L1 from Stenotrophomonas maltophilia [ 9 ] . A similar grouping scheme (B1, B2, and B3) based on structural properties of the metallo-β-lactamases has recently been offered [ 41 ] . The diversity of the group 3 β-lactamases is best exemplified by the enzymes' vastly differing efficacies towards non-clinical inhibitors; these differences predict that one inhibitor may not inhibit all metallo-β-lactamases [ 18 20 21 22 23 24 25 26 27 28 29 ] . To combat this problem, we are characterizing a metallo-β-lactamase from each of the subgroups in an effort to identify a common structural or mechanistic aspect of the enzymes that can be targeted for the generation of an inhibitor.

  • 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).

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