Nanosecond electron transfer kinetics in photosystem I following substitution of quinones for vitamin K1 as studied by time resolved EPR.
Room temperature transient EPR spectra of photosystem I (PS I) particles from Synechocystis 6803 are presented. Native PS I samples and preparations depleted in the A1-acceptor site by solvent extraction and then reconstituted with the quinones (Q) vitamin K1 (VK1), duroquinone (DQ and DQd12) and naphthoquinone (NQ) have been studied. Sequential electron transfer to P700+A1- (FeS) and P700+A1 (FeS)- is recovered only with VK1. With DQ and NQ electron transfer is restored to form the radical pair P700+Q- as specified by a characteristic electron spin polarization (ESP)-pattern, but further electron transfer is either slowed down or blocked. A qualitative analysis of the K-band spectrum suggests that the orientation of reconstituted NQ in PS I is different from the native acceptor A1 = VK1.
Sieckman
I
I
Fachbereich Physik, Freie Universität Berlin, Germany.
van der Est
A
A
Bottin
H
H
Sétif
P
P
Stehlik
D
D
D000458:Cyanobacteria / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D007700:Kinetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045331:Photosystem I Protein Complex; D011809:Quinones / Q000737:chemistry*; D010837:Vitamin K 1 / Q000737:chemistry*
D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D011809:Quinones; D010837:Vitamin K 1