Kinetics of Light-Induced Intramolecular Energy Transfer in Different Conformational States of NADH

Heiner, Zsuzsanna and Roland, Thomas and Leonard, Jérémie and Haacke, Stefan and Groma, Géza (2017) Kinetics of Light-Induced Intramolecular Energy Transfer in Different Conformational States of NADH. JOURNAL OF PHYSICAL CHEMISTRY B - CONDENSED MATTER MATERIALS SURFACES INTERFACES AND BIOPHYSICAL, 121 (34). pp. 8037-8045. ISSN 1520-6106

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Abstract

When bound to a protein, the coenzyme NAD+/NADH typically exists in an extended conformation, while in aqueous solutions it can be characterized by an equilibrium of folded and unfolded structures. It was recognized long ago that in the folded conformation light absorption at the adenine ring initiates an effective energy transfer (ET) toward the nicotinamide group, but the mechanism of this process is still unexplored. Here we apply ultrafast transient absorption measurements on NADH combined with compartmental model analysis for following the kinetics of the ET. We find that the actual ET is extremely rapid (similar to 70 fs). The high rate can be well described by a Forster-type mechanism, promoted by both.the special photophysical properties of adenine and the subnanometer inter-ring distance. The rapid ET creates a vibrationally hot excited state on nicotinamide, the vibrational and electronic relaxation of which is characterized by 1.7 and 650 ps, respectively.

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