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 a nd UV-vis spectroscopy. The results indicate that the BSA binding sites are very effective in hindering fast nonradiative relaxation processes that oc cur via rotational motion of the aromatic rings of this triarylmethane. As a result, pronounced increases in both fluorescence yield and dye photoreac tivity were observed upon protein binding. The 532 nm laser-induced photobl eaching of protein-bound MG(+) yields leuco malachite green and 4-dimethyla minobenzophenone as major reaction photoproducts. Based on the nature of th ese products, the first step of the bleaching process is postulated to be a n electron or hydrogen atom transfer from the protein to the dye moiety. (C ) 1999 Elsevier Science Ltd. All rights reserved.