CMTDP

CMTDP is a Fluorescent probe for detecting local polarity changes around the Cys34 domain of bovine serum albumin during pH-induced N→B conformational transition. It is a thiol-specific and polarity-sensitive probe; it covalently labels the free cysteine residue at position 34 (Cys34) of bovine serum albumin, and its fluorescence maximum emission wavelength shifts in response to solvent polarity, but not to pH and temperature. When labeled to BSA, as the local polarity around the Cys34 domain increases with rising pH, the probe shows a bathchromic shift in fluorescence emission wavelength and a decrease in fluorescence intensity, which allows quantification of the local polarity change via the relationship between emission wavelength shift and dielectric constant. CMTDP itself has absorption peaks at ~392 and 508 nm, and CMTDP-labeled BSA has excitation maxima at 376 and 470 nm at pH 6.0, with the shorter-wavelength excitation peak red-shifting as pH increases while the longer one remains stable; when excited at 470 nm, the fluorescence emission maximum shifts from 570 nm at pH 6.0 to 577 nm at pH 9.1, while free CMTDP at pH 7.4 has an emission maximum at 621 nm. The excitation/emission wavelengths for CMTDP-labeled BSA are Ex/Em = 376/570 nm at pH 6.0, Ex/Em = ~376+/573 nm at pH 7.4, Ex/Em = ~376+/575 nm at pH 8.0, Ex/Em = ~376+/577 nm at pH 9.1, and for free CMTDP at pH 7.4, Ex/Em (when excited at 470 nm) = 470/621 nm[1].