  The dynamics of polarized fluorescence in reduced nicotinamide adenine
dinucleotide (NADH) at 436~nm under two-photon excitation at 720~nm by
femtosecond laser pulses in alcohol dehydrogenase (ADH)-containing buffer
solution has been studied experimentally and theoretically. A global fit
procedure was used for determination of the fluorescence parameters from
experimental data. The interpretation of the experimental results obtained was
supported by \emph{ab initio} calculations of NADH structure in solutions. A
theoretical model was developed for description of the polarized fluorescence
decay in enzyme-NADH binary complexes that considered several possible
interaction scenarios. We suggest that the origin of a significant enhancement
of the nanosecond decay time value in the ADH-bounded NADH compare with the
free NADH can be attributed to the significant decrease of non-radiative
relaxation probabilities due to decrease of charges separations in the
nicotinamide ring in the conditions of an apolar ADH-NADH binding site
environment. The existence of a single decay time in the ADH-NADH complex in
the nanosecond time-domain in comparison with two decay times observed in free
NADH can be attributed to a single NADH unfolded \emph{trans}-like conformation
bounded within the ADH site. Comparison of the experimental data obtained and
the theory developed suggested the existence of an anisotropic relaxation time
of about 1 ns related most likely with interactions between excited NADH and
the ADH binding site that resulted in the rearrangement of nuclear distribution
and rotation of fluorescence transition dipole moment.
