Cysteine thiol probe

Cysteine Thiol Probe is a thiol-based probe designed to label electrophilic natural products. Cysteine Thiol Probe possesses each of the characteristics of an ideal pharmacophore probe, and has a chromophore. Cysteine Thiol Probe is capable of engaging enone-, β-lactam-, and β-lactone-based electrophilic metabolites .

Dibromobimane is a Fluorescent dye and probe that can be used for the detection of intracellular reduced glutathione and the analysis of spatial proximity of closely adjacent cysteine thiol groups. Dibromobimane activates fluorescence through binding to thiol groups; its excitation/emission wavelengths are Ex/Em = 393/477 nm for glutathione detection, and Ex/Em = 385/477 nm for cysteine thiol cross-linking. Dibromobimane uses two equivalent bromomethyl groups to cross-link cysteine thiolates with a distance ranging from 3-6 Å. Dibromobimane can be applied to 96-well microplate-based high-throughput assays for labeling intracellular glutathione, and its fluorescence signal is normalized against nuclear staining results to eliminate the impact of cell density .

BADAN is a thiol-reactive, environment-sensitive fluorescent probe used for site-specific labeling of protein cysteine residues to detect protein topology, local polarity, protein-lipid interactions, and conformational changes. The bromoacetyl group of BADAN covalently binds to cysteine thiols, and its fluorescence originates from the intramolecular charge transfer (ICT) excited state. The emission peak position varies with the polarity of the surrounding medium: it blue-shifts to approximately 488 nm in nonpolar environments (such as the hydrophobic core of lipid bilayers) and red-shifts to approximately 496-507 nm in polar environments (such as aqueous phases), independent of enzymes, pH, or membrane potential. Ex = 380-402 nm; Em = 400-600 nm .

TPEP-6-NH-MA is a Fluorescent probe that selectively detects cysteine (Cys) and homocysteine (Hcy) without interference from glutathione (GSH) and other amino acids, and can also be used for bioimaging of biothiols in living cells. Its detection mechanism relies on terminating the photoinduced electron transfer (PET) effect via a Michael addition reaction between the maleimide recognition moiety and the thiol group of Cys or Hcy. The excitation wavelength of TPEP-6-NH-MA is Ex = 361 nm .

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].