Spectroscopic and photochemical properties of Malachite Green noncovalently bound to bovine serum albumin

The noncovalent binding of the cationic triarylmethane dye Malachite Green (MG+) to bovine serum albumin (BSA) was investigated using fluorescence and UV-vis spectroscopy. The results indicate that the BSA binding sites are very effective in hindering fast nonradiative relaxation processes that occur via rotational motion of the aromatic rings of this triarylmethane. As a result, pronounced increases in both fluorescence yield and dye photoreactivity were observed upon protein binding. The 532 nm laser-induced photobleaching of protein-bound MG+ yields leuco malachite green and 4-dimethylaminobenzophenone as major reaction photoproducts. Based on the nature of these products, the first step of the bleaching process is postulated to be an electron or hydrogen atom transfer from the protein to the dye moiety.