Fluoresceins for Fluorescent Labeling

Fluorescein has been well-known as a green-fluorescent substance with the maximum absorption wavelength (494 nm) and the maximum fluorescence wavelength (521 nm). 1, 2 and 3 containing an isothiocyanate group can react and bond to an amino goup or a thiol group, so they are applied to the fluorescent labeling of enzymes, antibodies and peptides.¹⁾ By using 4 and 5 which have a carboxyl group, amino moieties such as the N-terminal of peptides are able to be labeled.²⁾ 6 is a N-substituted succinimide of 4, the carboxyl moiety of which reacts readily with an amino group under mild conditions. It has been reported that intracellular proteins are fluorescent-labeled by 6 when introduced into a cell.³⁾ 7 containing a maleimide group can easily bond to the thiol group of cysteine residue etc.⁴⁾ 8 and 9 can react with carboxyl moieties to form amide bonding in the presence of a condensation agent.⁵⁾