Abstract

This study examines acrylamide quenching of tryptophan room-temperature phosphorescence in proteins and the role that factors such as long-range interactions and environment-dependent quenching efficiency might play in the interpretation of bimolecular quenching rate constants in terms of hindered quencher migration through the globular fold. The distance dependence of the through-space quenching rate is evaluated by studying the effects of acrylamide on the phosphorescence intensity and decay kinetics of the indole analogue 2-(3-indoyl)ethyl phenyl ketone in propylene glycol/buffer glasses, at 120 K. Both steady-state and kinetic data are satisfactorily fitted by an exponential distance dependence of the rate, k(r) = k0 exp[−(r − r0)/re], with a contact rate k0 = 1.2 × 108 s-1 and an attenuation length re = 0.29 A. For a phosphorescence lifetime of 5 s, this rate yields an average interaction distance of 10 A. The rate is temperature dependent, with k0, estimated from the bimolecular quenching rate const...

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