Ultrafast dynamics of ligand and substrate interaction in endothelial nitric oxide synthase under Soret excitation

Abstract

Ultrafast transient absorption spectroscopy of endothelial NOS oxygenase domain (eNOS-oxy) was performed to study dynamics of ligand or substrate interaction under Soret band excitation. Photo-excitation dissociates imidazole ligand in <300 fs, then followed by vibrational cooling and recombination within 2 ps. Such impulsive bond breaking and late rebinding generate proteinquakes, which relaxes in several tens of picoseconds. The photo excited dynamics of eNOS-oxy with L-arginine substrate mainly occurs at the local site of heme, including ultrafast internal conversion within 400 fs, vibrational cooling, charge transfer, and complete ground-state recovery within 1.4 ps. The eNOS-oxy without additive is partially bound with water molecule, thus its photoexcited dynamics also shows ligand dissociation in <800 fs. Then it followed by vibrational cooling coupled with charge transfer in 4.8 ps, and recombination of ligand to distal side of heme in 12 ps. (C) 2016 Elsevier B.V. All rights reserved.