THE RATES OF PROTON UPTAKE AND ELECTRON-TRANSFER AT THE REDUCING SIDE OF PHOTOSYSTEM-II IN THYLAKOIDS

Proton 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 Q(A)FeQ(B) 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 Q(A)FeQ(B)(-) to the cytochrome b(6)f complex were constant. The half-rise times of electron transfer (tau(e)) and the apparent times of proton binding (tau(h)) at 30 mu M Neutral red were: Q(A)(-)double right arrow Fe(III)Q(B)(tau(e) less than or equal to 100 mu s, tau(h)=230 mu s); Q(A)(-)double right arrow Fe(II)Q(B)(tau(e)=150 mu s, tau(h)=760 mu s); and Q(A)(-)double right arrow Fe(II)Q(B)(-)(tau(e)=620 mu s, tau(h)=310 mu s).