Two photon-induced electron injection from a nanotrigger in native endothelial NO-synthase.

We have recently designed a nanotrigger (NT), a photoactive molecule addressing the NADPH sites of proteins. This nanotrigger has a 10(3) times larger two-photon cross-section compared to the ubiquitous NADPH cofactor. In this work, we tested whether two-photon excitation of the bound NT to NADPH sites may be used to initiate enzymatic catalysis by appropriate electron injection. To establish proof of principle, we monitored the ultrafast absorption of NT bound to the fully active endothelial NO-Synthase (eNOS) following excitation by one and two-photons at 405 and 810 nm, respectively. Electron injection from NT* to FAD in eNOS initiated the catalytic cycle in 15+/-3 ps at both exciting wavelengths. The data proved for the first time that electron transfer can be promoted by two-photon excitation. We also show that the nanotrigger decays faster in homogeneous solvents than in the NADPH site of proteins, suggesting that hindered environments modified the natural decay of NT. The nanotrigger provides a convenient way of synchronizing an ensemble of proteins in solution with a femtosecond laser pulse. The ability of NT to initiate NOS catalysis by two-photon excitation may be exploited for controlled and localized release of free NO in cells with enhanced spatial and temporal resolution.