Electron transfer kinetics in photosynthetic reaction centers embedded in polyvinyl alcohol films.
The coupling between electron transfer and protein dynamics has been studied at room temperature in isolated reaction centers (RCs) from the photosynthetic bacterium Rhodobacter sphaeroides by incorporating the protein in polyvinyl alcohol (PVA) films of different water/RC ratios. The kinetic analysis of charge recombination shows that dehydration of RC-containing PVA films causes reversible, inhomogeneous inhibition of electron transfer from the reduced primary quinone acceptor (Q(A)(-)) to the secondary quinone Q(B). A more extensive dehydration of solid PVA matrices accelerates electron transfer from Q(A)(-) to the primary photooxidized electron donor P(+). These effects indicate that incorporation of RCs into dehydrated PVA films hinders the conformational dynamics gating Q(A)(-) to Q(B) electron transfer at room temperature and slows down protein relaxation which stabilizes the primary charge-separated state P(+)Q(A)(-). A comparison with analogous effects observed in trehalose-coated RCs suggests that protein motions are less severely reduced in PVA films than in trehalose matrices at comparable water/RC ratios.
Francia
Francesco
F
Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy.
Giachini
Lisa
L
Palazzo
Gerardo
G
Mallardi
Antonia
A
Boscherini
Federico
F
Venturoli
Giovanni
G
D000042:Absorption; D004579:Electron Transport / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D008567:Membranes, Artificial; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000528:radiation effects*; D011142:Polyvinyl Alcohol / Q000737:chemistry*; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D014867:Water / Q000737:chemistry*
D008567:Membranes, Artificial; D045322:Photosynthetic Reaction Center Complex Proteins; D014867:Water; D011142:Polyvinyl Alcohol