Light-induced charge separation in Photosystem I at low temperature is not influenced by vitamin K-1.
The photoreduction of iron-sulfur centers was studied at low temperature in Photosystem I particles from spinach and the cyanobacterium Synechocystis 6803, which contain various amounts of vitamin K-1 (recently tentatively identified as the acceptor A1). The irreversible charge separation that was progressively induced at low temperature between P-700 and FA (or FB) by successive laser flashes was studied at 15 K. Its maximum amount after a large number of flashes was shown to be fairly independent of the number (0, 1 or 2) of vitamins K-1 per reaction center. Moreover, the first flash yield of this charge separation was diminished by only about 50% when vitamin K-1 was completely absent from the particles by comparison with particles containing one or two vitamin K-1 per reaction center. When FA and FB were prereduced, the iron-sulfur center FX was also reversibly photoreduced at 9 K in the absence of vitamin K-1. The implications of these results for the electron pathways of Photosystem I are discussed and it is proposed that a direct electron transfer from A0- to the iron-sulfur centers is highly efficient at low temperature.
Sétif
P
P
Département de Biologie, C.E.N. Saclay, Gif-sur-Yvette, France.
Ikegami
I
I
Biggins
J
J
D002734:Chlorophyll / Q000502:physiology*; D004578:Electron Spin Resonance Spectroscopy; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000502:physiology*; D013696:Temperature; D010837:Vitamin K 1 / Q000494:pharmacology*
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D010837:Vitamin K 1