Photosynthetic water oxidation under flashing light. Oxygen release, proton release and absorption transients in the near ultraviolet — A comparison between thylakoids and a reaction-centre core preparation

Photosynthetic oxygen evolution: Net charge transients as inferred from electrochromic bandshifts are independent of proton release into the medium

“…The pattern of the pH transient oscillated and differed depending on the pH. At pH 5.5 the extent on the first flash was larger than the one on the third whereas at pH 7.0 this was reversed, as documented elsewhere [3,4]. The patterns uf the electrochromic transients, on the other hand, were similar at both pH values and similar to the ones obtained with core particles.…”

“…These variations are not paralled by variations of the pattern of oxygen evolution and of the UV transients, which are indicative of manganese redox transitions [3]. In this work we investigated the pattern of electrochromic transients which might reflect the net charge transients of the catalytic center as the result of electron abstraction and proton release.…”

“…The superimposed electrochromic bandshifts due to Qa formation are non-oscillating under the given electron acceptor conditions (see below). They were recorded under repetitive excitation (repetition period: 5 s thylakoids, 0.2 s core particles) and then subtracted from the former ones (see [3]). With thylakoids the media contained 2.6 g/l BSA, with core particles 10 mM MES as pH buffer.…”

“…This steps the manganese cluster from state So (the most reduced state) to S,, which spontaneously decays into S, under release of dioxygen. The distribution of the four protons over the redox transitions varies strongly depending on the pH and on the type of PSI1 preparation (see [2] for a review) whereas the pattern of oxygen evolution is invariant [3]. Under certain conditions the major portion of proton release occurs in some 10 ,us, before the electron hole is deposited on the manganese cluster, i.e.…”

Chloride‐depletion of photosynthetic water oxidase

“…Fax: (49) (541) 969 2870. Internet: junge@sfb.biologie.uni-osnabrueck.DE different stoichiometric patterns between BBY-membranes [3], unperturbed thylakoids [4,5], thylakoids which are depleted of the light harvesting complexes [6] and PS II-core preparations [4,7,8]. The primary electron donor of PS II, P&, oxidises the manganese cluster via an intermediate carrier, Tyrz (for review see [2]).…”