1974). As suggested by Johnson and Ruban (2013) also voltage-gated anion (Schönknecht et al. 1988) and cation (Pottosin and Schönknecht 1996) channels could be involved. Fast DIRK recording and new technique of continuously measured charge flux For the DIRK analysis demonstrated in Fig. 2b the P515 signal was recorded with a time resolution of 10 ms/point, which is more than sufficient to determine the amplitude of the rapid negative transient peaking around 350 ms after light-off. A much higher time resolution is required to resolve the initial
kinetics of the rapid negative transient. Figure 3 CFTR inhibitor shows a screenshot of a recording with 0.1 ms/point resolution (Fig. 3). Fig. 3 Recording of the fast decay phase of the DIRKECS selleck screening library response with indication of the initial slope reflecting the rate of charge flux briefly before light-off The initial slope of the dark-interval ECS-decay carries twofold information on the rate of photosynthetic charge fluxes, in terms of both electron and proton transport (Cruz et al. 2001; Sacksteder et al. 2001; Joliot and Joliot 2002; Joliot et al. 2004). Light-driven vectorial electron transport is coupled with proton transport from the stroma to the lumen, which is balanced by proton efflux via the ATP synthase, so that ECS in a quasi-stationary
state is constant (zero rate of ECS change, R light = 0). Upon light-off, the light-driven reactions stop, whereas proton efflux continues in the dark. Furthermore, it has to be considered that the light-driven electrogenic reactions not only involve charge separation at PS II and PS I, but also selleck chemicals llc vectorial proton translocation from the stroma to the lumen in the Q-cycle at the cyt b6f complex (Velthuys 1978). If it is assumed that the rate of the Q-cycle is not appreciably changed during the first ms after light-off (Joliot and Joliot 2002), it follows for the ECS changes in a quasi-stationary light state briefly before and after light-off, R light and R dark, respectively (Joliot et al. 2004): (1) R light is proportional to R ph + R bf − R efflux, with R ph being the overall rate of photochemical charge separation in PS I and PS II, R
bf the rate of proton translocation coupled with cyt bf turnover and R efflux the rate of proton efflux via the ATP synthase. (2) R dark is proportional to R bf − R efflux, as R ph = 0. (3) Dichloromethane dehalogenase R light − Rdark is proportional to R ph + R bf − R efflux − (R bf − R efflux) = R ph. If in a quasi stationary light state positive and negative electrogenic reactions are balanced, as in the experiment of Fig. 3, R light = 0 and R dark is directly proportional to R ph. Furthermore, R dark is also a measure of the rate of proton efflux via the ATP ase, i.e., proportional to the rate of ATP synthesis. However, as apparent from point (2) above, the proportionality only holds as long as it is assumed that the Q-cycle is obligatory (Sacksteder et al. 2000).