Fig 3.
β-Lactamase production in E. coli DH5α strains harboring the plasmids pNSP1bla (no signal peptide [noSP]), pCSP1bla (CSP), and the 12 different plasmids pCSP1S2bla-pCSP1S61bla (CSP mutants S2 to S61). Gene expression was induced by 0.1 mM m-toluic acid. (a) Specific β-lactamase activities measured from cell extracts. 1 U = the amount of enzyme that catalyzes the transformation of 1 μmol of substrate min−1. The results are the averages of two biological replicas performed in triplicates, and the standard errors are indicated. (b) Western blot detection of soluble β-lactamase in the same extracts as in panel a. The same total protein amount was applied in all wells. The sizes of the mature and the uncleaved β-lactamase proteins are approximately 29 and 32 kDa, respectively. The two boxes show independent blots; vertical lines within the boxes indicate that one or more samples have been removed from the data set. The M column represents the migration of ladder proteins of sizes 25, 37, and 50 kDa, respectively.