Fluorescence decay times: proteins, coenzymes, and other compounds in water.

The fluorescence decay time (tau) was 2 to 5 nanoseconds for proteins and 4 to 5 nanoseconds for flavin, pyridine nucleotide, and vitamin B(6)coenzymes; tau varied widely in 48 compounds measured in water. Altholugh reported values of tau for a few of the soluttions studied were in excellenlt agreement. previously "calculated" lifetimes, in severall instances, are apparently erroneous. Nonexponential decay was detectable with our "nanosecond-flash" apparatus, a modification of the first commercially aavilable unit for determination of tau.