9-Vinylacridine as a New Reagent for Determination of Sulfhydryl Groups in Proteins and the Spectrophotometric Studies

A fluorescent reagent 9-vinylacridine reacted with sulfhydryl group of cysteine to yield S-β-(9-acridinylethyl)-l-cysteine which absorbed ultraviolet light with a molar extinction coefficient of 17,500 at 358 nm and emitted strong fluorescence in aqueous acetic acid.9-Vinylacridine also reacted quantitatively with sulfhydryl groups of reduced lysozyme and reduced ribonuclease in acidic condition to give acridinylethylared proteins. This reaction enabled determination of sulfhydryl groups in proteins. From the ultraviolet absorption and the fluorescence characteristics of acridinylethylated proteins, the polarity of the environment of cysteine residues were discussed.