LABELING OF SULFHYDRYL-GROUPS IN INTACT MAMMALIAN-CELLS WITH COUMARINS

4-(Bromomethyl)-6,7-dimethoxy-2-oxo-2H-benzopyran (1) and its 3-[I-125 ]iodo derivative (2) were reacted with sulfhydryl groups of proteins i n viable Chinese hamster V79 lung fibroblasts. Pretreatment of cells w ith dithiothreitol (DTT) as the reducing agent was necessary to give d etectable levels of fluorescence. In the absence of DTT, V79 cells inc orporated about 1 X 10(-3) pCi/Cell of the ratioiodinated, no-carrier- added derivative; following incubation of cells with 320 muM DTT the u ptake was nearly doubled (1.87 X 10(-3) pCi/cell).