N-(3-pyrene)maleimide: a long lifetime fluorescent sulfhydryl reagent.

We report the chemical synthesis and some useful applications of N-(3-pyrene)maleimide which forms fluorescent adducts with organic compounds and proteins which contain sulfhydryl groups. Lifetime of the first excited singlet state of the small molecule adducts ranged from 1.4 to 6.5 ns. Fluorescence of the protein adducts exhibited two distinct lifetimes for each adduct. The longer component had a value of about 100 ns. Because of the long lifetime, N-(3pyrene)maleimide is useful for fluorescence polarization studies of high molecular weight proteins and other macromolecules having reactive sulfbdryl groups.