Fig. 2.

The product (end of reaction) IR difference spectrum vs. free protein of the acylprotein formed at 22°C between ampicillin and BlaR. BlaR^S (0.6 mM) was mixed with 0.6 mM ampicillin, both dissolved in reaction buffer, pH meter reading 7.5, in the stopped-flow apparatus. Sample spectra (8,320), four replicates, and 2,080 reference (one replicate) spectra were used to construct the difference spectrum. Solid line, experimental data; dashed line, overall fitted line; gray lines, individual fitted bands. (Inset) A magnified version of the acyl-protein ester band at 1,732 cm⁻¹. Both sample and reference spectra were constructed from three replicate experiments by averaging 6,240 spectra at 4-cm⁻¹ resolution. The band-fitting parameters are given in Table 2, together with values obtained from an equivalent stopped-flow experiment.