Reaction of fluorogenic reagents with proteins. III. Spectroscopic and electrophoretic behavior of proteins labeled with Chromeo P503

The spectroscopic and electrophoretic properties of proteins labeled with Chromeo P503 were investigated. Its photobleaching characteristics were determined by continually infusing Chromeo P503-labeled α-lactalbumin into a sheath-flow cuvette and monitored fluorescence as a function of laser power. The labeled protein is relatively photo-labile with an optimum excitation power of about 2 mW. The unreacted reagent is weakly fluorescent but present at much higher concentration than the labeled protein. The unreacted reagent undergoes photobleaching at a laser power more than an order of magnitude higher than the labeled protein. One-dimensional capillary electrophoresis analysis of Chromeo P503-labeled α-lactalbumin produced concentration detection limits (3σ) of 12 pM and mass detection limits of 0.7 zmol, but with modest theoretical plate counts of 17,000. The reagent was employed for the two-dimensional capillary electrophoresis analysis of a homogenate prepared from a Barrett's esophagus cell line; the separation quality is similar to that produced by 3-(2-furoyl)quinoline-2-carboxaldehyde (FQ), a more commonly used reagent.