FIG. 4.

Fluorescence excitation spectra of Φ(gfp-cbbS)(Hyb)::Kan^r mutant carboxysomes. Equivalent amounts (mg of protein) of purified mutant carboxysomes were suspended in buffers of the pH values indicated in the graph. Fluorescence emission intensity above 495 nm was recorded as excitation wavelengths from 400 to 480 nm were scanned. The scale on the ordinate axis represents voltage output from the spectrofluorometer. A pH-sensitive maximum was observed at 469 nm.