A rapid and simple 8-quinolinol-based fluorescent stain of phosphoproteins in polyacrylamide gel after electrophoresis

In order to obtain an easy and rapid protocol to visualize phosphoproteins in SDS-PAGE, a fluorescent detection method named 8-Quinolinol (8-Q) stain is described. 8-Q can form ternary complexes in the gel matrix contributed by the affinity of aluminum ion (Al(3+) ) to the phosphate groups on the proteins and the metal chelating property of 8-Quinolinol, exhibiting strong fluorescence in ultraviolet light. It can visualize as little as 4∼8 ng of α-casein and β-casein, 16∼32 ng of ovalbumin and κ-casein which is more sensitive than Stains-All but less sensitive than Pro-Q Diamond. The protocol of 8-Q requires only 70 min in 0.75 mm mini-size or 1.0 mm large-size gels with five changes of solutions without destaining step; Pro-Q takes at least 250 min with 11 changes of solutions. In addition, the new method was confirmed by the study of dephosphorylation and LC-MS/MS, respectively. The approach to visualize phosphoprotein utilizing 8-Q could be an alternative to simplify the analytical operations for phosphoproteomics research.