PMC

Fig. 4P700 kinetic traces and light saturation curves of P700 photooxidation of isolated PSI monomers and trimers, from cells grown under increased photon flux (FL). PSI was isolated from WT and ORR1 cells using anion-exchange chromatography. (A) The kinetic trace of P700 at 2000 μmol photons per m2 per s. Measurements used equivalent P700. (B) The maximum value of P700 photooxidation was measured at different actinic light intensity (200 to 2000 μmol photons per m2 per s). Values were normalized to maximum WT photooxidation (trimers were normalized to WT trimers, monomers were normalized to WT monomers). WT: black, ORR1: red, PSI trimers: solid line, PSI monomers: dashed line.

Fig. 7Pump (630 nm)–probe (810 nm) data for solubilized PSI indicate that: (a) charge recombination from FB− to P700+ is seen in the presence of ascorbate (purple) due to the slow kinetics of this donor. Addition of methyl viologen (orange) scavenges electrons and maintains the P700+ population. The subsequent addition of DCPIP as a donor reduces P700+ at relevant timescales; (b) if the chlorophyll network is disrupted by denaturing agents such as SDS detergents or ethanol, no P700+ is formed at any time.

Fig. 7

Fig. 2Photochemical properties of PSI reaction centers isolated from WT and ORR1 strains. (A) P700 kinetic traces of isolated PSI monomers and trimers from WT and ORR1, measured at 2000 μmol photons per m2 per s. (B) Light saturation curves of PSI monomers and trimers from WT and ORR1, normalized to equivalent P700 concentrations. Maximal P700 photooxidation amplitude was plotted against actinic light intensity (200 to 5000 μmol photons per m2 per s). Values were normalized to maximum WT photooxidation (trimers were normalized to WT trimers, monomers were normalized to WT monomers). WT: black, ORR1: red, PSI trimers: solid line, PSI monomers: dashed line.