FLUORESCENCE DECAY STUDIES OF REDUCED NICOTINAMIDE ADENINE-DINUCLEOTIDE IN SOLUTION AND BOUND TO LIVER ALCOHOL-DEHYDROGENASE

The monophoton counting technique was used to obtain the fluorescence decay kinetics of NADH bound to LADH (horse liver alcohol dehydrogenase). The fluorescence decay of the enzyme complex did not follow a single exponential decay law but the data could be well described as a sum of 2 exponentials. The decay parameters of the enzyme complex do not depend on the degree of binding-site saturation. These results are interpreted in terms of a reversible excited-state reaction forming a nonfluorescent product. Fluorescence decay kinetics are also reported for NADH and related molecules in solution. The decay parameters, fluorescence emission maxima, and fluorescence intensities depend on solvent polarity and viscosity.