Steady-state kinetic analyses of the Photosystem II activity elicited by quinones and quinonediimines in KCN/Hg-inhibited chloroplasts reveal that: 1. Quinones generate a single reaction in which one quinone competes with another for photoreduction by Photosystem II. 2. Quinonediimines also compete with one another for photoreduction, but the electron transport activity elicited by quinonediimi...

Prochlorococcus and Synechococcus picocyanobacteria are dominant contributors to marine primary production over large areas of the ocean. Phytoplankton cells are entrained in the water column and are thus often exposed to rapid changes in irradiance within the upper mixed layer of the ocean. An upward fluctuation in irradiance can result in photosystem II photoinactivation exceeding counteracti...

Photosystem II reaction centers comprised of the Dl, D2 and cytochrome b-559 polypeptides were isolated from welldefined oxygen-evolving reaction center preparations using either a combination of LiClO, and dodecyhnaltoside, or Triton X-100 alone. Yields of chlorophyll and cytochrome b-559 for both preparative methods were compared, and pigment contents were compared based on 2.0 b-559 per reac...

Illumination of intact Bryopsis corticulans chloroplasts under anaerobic conditions induced a decline of chlorophyll fluorescence and photoinhibition of Photosystems I and II. The time course of the light-induced decline of chlorophyll fluorescence and the decreases of activities of reactions sensitized by Photosystems I and II were compared. Photosystem I activity decreased in parallel with th...

The structural and topological stability of thylakoid components under photoinhibitory conditions (4,500 microE.m-2.s-1 white light) was studied on Mn depleted thylakoids isolated from spinach leaves. After various exposures to photoinhibitory light, the chlorophyll-protein complexes of both photosystems I and II were separated by sucrose gradient centrifugation and analysed by Western blotting...

Photosystem II, Active Particles, Polypeptides, Thylakoid Membrane, Anacystis A thylakoid membrane preparation isolated from the blue-green alga Anacystis nidulans was freed from carboxysomes, soluble enzymes and the pigment P750 by floating in a discontinuous sucrose density gradient. In a buffer containing sucrose and the zwitterionic detergent Miranol S2M-SF the thylakoids were loaded on a l...

Photosynthetic organisms experience changes in light quantity and light quality in their natural habitat. In response to changes in light quality, these organisms redistribute excitation energy and adjust photosystem stoichiometry to maximize the utilization of available light energy. However, the response of other cellular processes to changes in light quality is mostly unknown. Here, we repor...

Photosystem II is a multisubunit pigment-protein complex embedded in the thylakoid membranes of chloroplasts. It utilizes light for photochemical energy conversion, and is heavily involved in the regulation of the energy flow. We investigated the structural organization of photosystem II and its associated light-harvesting antenna by electron microscopy, multivariate statistical analysis, and c...

An intrinsic 22 kDa polypeptide is associated with the O2-evolving Photosystem II core complex in a variety of green plants, although it does not appear to be required for O2 evolution. Digestion of thylakoid membranes and isolated Photosystem II preparations with trypsin, followed by immunoblotting using spinach anti-22 kDa antibodies, leads to two observations: (1) the domain between the 2nd ...

As was described previously, an antiserum to polypeptide 11000 inhibited photosynthetic electron transport on the oxygen evolving side of photosystem II. The effect of the antiserum on chloroplasts from two tobacco mutants also clearly showed that the inhibition site is on the photosystem II-side of the electron transport chain. One of the two tobacco mutants lacks the oxygen evolving capacity ...