FIG. 7.

Preferential interaction of Flu-APA with the 85-kDa PBP. Increasing concentrations of Flu-APA were incubated for 15 min with a membrane preparation from a culture of S. griseus that had entered stationary phase (A₅₀₀ = 12) in glucose-ammonia minimal medium supplemented with 1% casein hydrolysate. (Membranes prepared from this culture contained relatively high amounts of the 66- and 140-kDa PBPs, which permitted more accurate quantitation of their levels.) Band intensities were measured as described in Materials and Methods, the background was subtracted, and the results were fit to a hyperbolic curve (one binding site) by using Prism 2.01 (GraphPad, San Diego, Calif.). By this analysis, the relative K_d of the 85-kDa PBP (×) was 2.3- and 2.7-fold lower than that of the 66 (○)- and 140 (•)-kDa PBPs, respectively; the coefficients of determination (r²), which indicate the fit of the data to the equation, were 0.9694 (66-kDa PBP), 0.9892 (85-kDa PBP), and 0.9602 (140-kDa PBP).