Fluorescence and protein structure: XI. Fluorescence quenching by disulfide and sulfhydryl groups

Abstract

1. 1.|Compounds were synthesized as models for quenching of tryptophan and tyrosine fluorescence in proteins. Bis-indole-3-methylene disulfide, bis-4-methoxybenzyl disulfide and their corresponding reduced, sulfhydryl derivatives were of extremely low fluorescence. The loss of fluorescence is ascribed to internal quenching by the disulfide and sulfhydryl groups. 2. 2.|Similar results were obtained for l-cystinyl-bis- l-tyrosine, HOOC(CH 2) 2-S-S-Cys-Tyr, ribonuclease-(SCH 2CH 2COOH) 8, and their reduced or carboxy-methylated products. That is, the disulfide group strongly quenched the fluorescence; the reduced sulfhydryl group quenched less. 3. 3.|The mechanism of quenching has not been established but several of the common pathways were rejected. The most probable mechanism seems to be an extremely short-range interaction between the aromatic ring and the sulfur atoms that facilitates a vibrational dissipation of the excitation energy.