FIGURE 3.

DAPI fluorescence in the presence of purified ATP and poly P. Fluorescence was excited at 405 nm and emission was monitored simultaneously at 475 and 550 nm. Arrows indicate points of addition of 6 μm poly P and 1.25 mm ATP. The change in DAPI fluorescence in response to ATP addition is larger when emission is measured 475 nm as compared with 550 nm. Subsequent addition of poly P substantially increased the 550-nm emission fluorescence while reducing the 475-nm emission fluorescence, consistent with a shift in DAPI-poly P emission spectrum. Addition of hexokinase to convert all the ATP in the cuvette to ADP reduced the fluorescence emission at 475 nm without any measurable effect on the 550 nm emission.