Temperature dependence of the disulfide perturbation to the triplet state of tryptophan.

Variability in the temperature dependence of disulfide quenching of the tryptophan phosphorescence of globular proteins in rigid glasses is illustrated with lysozyme and alpha-bungarotoxin. A laser-pulsed phosphorescence study of this short-range interaction with a model indole-disulfide system is described. The perturbation of secondary dibutyl disulfide on the triplet state of the indole moiety in 2-(3-indolyl)ethyl phenyl ketone in rigid media is found to display a bimodal temperature dependence. The quenching rate constant at contact between chromophore and perturber is observed to be temperature independent below 30 K, but to increase with temperature between 30 and 100 K with an activation energy of approximately 200 cm(-1). The results suggest that the underlying quenching interaction involves a photo-induced one-electron transfer from the excited state of indole to the disulfide.