Picosecond photoreduction of inducible nitric oxide synthase by rhenium(I)-diimine wires.
In a continuing effort to unravel mechanistic questions associated with metalloenzymes, we are developing methods for rapid delivery of electrons to deeply buried active sites. Herein, we report picosecond reduction of the heme active site of inducible nitric oxide synthase bound to a series of rhenium-diimine electron-tunneling wires, [Re(CO)3LL']+, where L is 4,7-dimethylphenanthroline and L' is a perfluorinated biphenyl bridge connecting a rhenium-ligated imidazole or aminopropylimidazole to a distal imidazole (F8bp-im (1) and C3-F8bp-im (2)) or F (F9bp (3) and C3-F9bp (4)). All four wires bind tightly (Kd in the micromolar to nanomolar range) to the tetrahydrobiopterin-free oxidase domain of inducible nitric oxide synthase (iNOSoxy). The two fluorine-terminated wires displace water from the active site, and the two imidazole-terminated wires ligate the heme iron. Upon 355-nm excitation of iNOSoxy conjugates with 1 and 2, the active site Fe(III) is reduced to Fe(II) within 300 ps, almost 10 orders of magnitude faster than the naturally occurring reduction.
Belliston-Bittner
Wendy
W
Beckman Institute, California Institute of Technology, Pasadena, California 91125, USA.
Dunn
Alexander R
AR
Nguyen
Yen Hoang Le
YH
Stuehr
Dennis J
DJ
Winkler
Jay R
JR
Gray
Harry B
HB
D000818:Animals; D001665:Binding Sites; D004579:Electron Transport; D006418:Heme / Q000737:chemistry; D007097:Imines / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D049449:Luminescence; D052247:Nitric Oxide Synthase Type II / Q000737:chemistry* / Q000528:radiation effects*; D010084:Oxidation-Reduction; D010777:Photochemistry / Q000379:methods*; D012211:Rhenium / Q000737:chemistry*; D014466:Ultraviolet Rays
D007097:Imines; D006418:Heme; D012211:Rhenium; D007501:Iron; D052247:Nitric Oxide Synthase Type II