The rates of proton uptake and electron transfer at the reducing side of photosystem II in thylakoids

AbstractProton and electron transfer at the reducing side of photosystem II of green plants was studied under flashing light, the former at improved time resolution by using Neutral red. The rates of electron transfer within QAFeQB were determined by pump-probe flashes through electrochromic transients. The extent of proton binding was about 1 H+/e−. The rates of proton transfer were proportional to the concentration of Neutral red (collisional transfer), whereas the rates of electron transfer out of Q−A and from QAFeQ−B to the cytochrome b6f complex were constant. The half-rise times of electron transfer (τe) and the apparent times of proton binding (τh) at 30 μM Neutral red were: Q−A ⇒ FeIIIQB (τe ⩽ 100 μs, τ, 230 μs); Q−A ⇒ FeIIQB (τe = 150 μs, τh = 760 μs); and Q−A ⇒ FeIIQ−B (τe = 620 μs, τh = 310 μs)