Nanosecond photoreduction of cytochrome p450cam by channel-specific Ru-diimine electron tunneling wires.
We report the synthesis and characterization of Ru-diimine complexes designed to bind to cytochrome p450cam (CYP101). The sensitizer core has the structure [Ru(L(2))L'](2+), where L' is a perfluorinated biphenyl bridge (F(8)bp) connecting 4,4'-dimethylbipyridine to an enzyme substrate (adamantane, F(8)bp-Ad), a heme ligand (imidazole, F(8)bp-Im), or F (F(9)bp). The electron-transfer (ET) driving force (-deltaG degrees ) is varied by replacing the ancillary 2,2'-bipyridine ligands with 4,4',5,5'-tetramethylbipyridine (tmRu). The four complexes all bind p450cam tightly: Ru-F(8)bp-Ad (1, K(d) = 0.077 microM); Ru-F(8)bp-Im (2, K(d) = 3.7 microM); tmRu-F(9)bp (3, K(d) = 2.1 microM); and tmRu-F(8)bp-Im (4, K(d) = 0.48 microM). Binding is predominantly driven by hydrophobic interactions between the Ru-diimine wires and the substrate access channel. With Ru-F(8)bp wires, redox reactions can be triggered on the nanosecond time scale. Ru-wire 2, which ligates the heme iron, shows a small amount of transient heme photoreduction (ca. 30%), whereas the transient photoreduction yield for 4 is 76%. Forward ET with 4 occurs in roughly 40 ns (k(f) = 2.8 x 10(7) s(-)(1)), and back ET (Fe(II) --> Ru(III), k(b) approximately 1.7 x 10(8) s(-)(1)) is near the coupling-limited rate (k(max)). Direct photoreduction was not observed for 1 or 3. The large variation in ET rates among the Ru-diimine:p450 conjugates strongly supports a through-bond model of Ru-heme electronic coupling.
Dunn
Alexander R
AR
Beckman Institute, California Institute of Technology, Pasadena, California 91125, USA.
Dmochowski
Ivan J
IJ
Winkler
Jay R
JR
Gray
Harry B
HB
D019475:Camphor 5-Monooxygenase / Q000737:chemistry*; D004583:Electrons; D006418:Heme / Q000031:analogs & derivatives; D007097:Imines / Q000138:chemical synthesis / Q000737:chemistry*; D007700:Kinetics; D008163:Luminescent Measurements; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D010777:Photochemistry; D012428:Ruthenium / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
D007097:Imines; D009942:Organometallic Compounds; D006418:Heme; D012428:Ruthenium; D019475:Camphor 5-Monooxygenase