Calcium reconstitutes high rates of oxygen evolution in polypeptide depleted Photosystem II preparations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/116911/1/feb20014579384808467.pd

On the role of water‐soluble polypeptides (17, 23 kDa), calcium and chloride in photosynthetic oxygen evolution

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/116934/1/feb20014579385800302.pd

Purification and properties of an oxygen-evolving reaction center complex from photosystem II membranes : A simple procedure utilizing a non-ionic detergent and elevated ionic strength

A method is reported for the isolation of a highly resolved oxygen-evolving photosystem II reaction center preparation. This preparation can be separated from the more complex photosystem II membranes isolated by the procedure of Berthold et al. [(1981) FEBS Lett. 134, 231-234] by use of octylglucopyranoside at elevated ionic strengths; the oxygen-evolving material can be collected by centrifugation at relatively low g values (40000 x g) in yields estimated to be more than 80%. This new preparation lacks the 17 and 23 kDa extrinsic polypeptides; addition of calcium and chloride produces activities approaching 1000 [mu]mol O2/h per mg chlorophyll. Although activity is maximal in the presence of 2,5-dichloro-[beta]-benzoquinone, the response of activity to ferricyanide and 3-(3,4-dichlorophenyl)-1,1-dimethylurea indicates that the reducing side of photosystem II has been modified in this new oxygen-evolving reaction center preparation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26236/1/0000316.pd

Polypeptides of photosystem II and their role in oxygen evolution

The linear, four-step oxidation of water to molecular oxygen by photosystem II requires cooperation between redox reactions driven by light and a set of redox reactions involving the S-states within the oxygen-evolving complex. The oxygenevolving complex is a highly ordered structure in which a number of polypeptides interact with one another to provide the appropriate environment for productive binding of cofactors such as manganese, chloride and calcium, as well as for productive electron transfer within the photoact. A number of recent advances in the knowledge of the polypeptide structure of photosystem II has revealed a correlation between primary photochemical events and a ‘core’ complex of five hydrophobic polypeptides which provide binding sites for chlorophyll a, pheophytin a, the reaction center chlorophyll (P680), and its immediate donor, denoted Z. Although the ‘core’ complex of photosystem II is photochemically active, it does not possess the capacity to evolve oxygen. A second set of polypeptides, which are water-soluble, have been discovered to be associated with photosystem II; these polypeptides are now proposed to be the structural elements of a special domain which promotes the activities of the loosely-bound cofactors (manganese, chloride, calcium) that participate in oxygen evolution activity. Two of these proteins (whose molecular weights are 23 and 17 kDa) can be released from photosystem II without concurrent loss of functional manganese; studies on these proteins and on the membranes from which they have been removed indicate that the 23 and 17 kDa species from part of the structure which promotes retention of chloride and calcium within the oxygen-evolving complex. A third water-soluble polypeptide of molecular weight 33 kDa is held to the photosystem II ‘core’ complex by a series of forces which in some circumstances may include ligation to manganese. The 33 kDa protein has been studied in some detail and appears to promote the formation of the environment which is required for optimal participation by manganese in the oxygen evolving reaction. This minireview describes the polypeptides of photosystem II, places an emphasis on the current state of knowledge concerning these species, and discusses current areas of uncertainty concerning these important polypeptides.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43541/1/11120_2004_Article_BF00037001.pd

Factors influencing hydroxylamine inactivation of photosynthetic water oxidation

The kinetics of Mn release during NH2OH inactivation of the water oxidizing reaction is largely insensitive to the S-state present during addition of NH2OH. This appears to reflect reduction by NH2OH of higher S-states to a common more reduced state (S0 or S-1) which alone is susceptible to NH2OH inactivation. Sequences of saturating flashes with dark intervals in the range 0.2-5 s-1 effectively prevent NH2OH inactivation and the associated liberation of manganese. This light-induced protection disappears rapidly when the dark interval is longer than about 5 s. Under continuous illumination, protection against NH2OH inactivation is maximally effective at intensities in the range 103-104 erg [middle dot] cm-2 [middle dot] s-1. This behavior differs from that of NH2OH-induced Mn release, which is strongly inhibited at all intensities greater than 103 erg [middle dot] cm-2 [middle dot] s-1. This indicates that two distinct processes are responsible for inactivation of water oxidation at high and low intensities. Higher S-states appear to be immune to the reaction by which NH2OH liberates manganese, although the overall process of water oxidation is inactivated by NH2OH in the presence of intense light. The light-induced protection phenomenon is abolished by 50 [mu]M DCMU, but not by high concentrations of carbonyl cyanide m-chlorophenylhydrazone, which accelerates inactivation reactions of the water-splitting enzyme, Y (an ADRY reagent). The latter compound accelerates both inactivation of water oxidation and manganese extraction in the dark.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24428/1/0000699.pd

Evidence for two cyclic photophosphorylation reactions concurrent with ferredoxin-catalyzed non-cyclic electron transport

Addition of ferredoxin to isolated spinach chloroplast thylakoid membranes reconstitutes phosphorylating electron transfer characterized by elevated P/O ratios (1.6). When oxygen is the terminal electron acceptor for reduced ferredoxin, the P/O value is lowered by antimycin A or low concentrations (10 [mu]M) of heparin (an anionic macromolecule), but not by inhibition of the activity of membrane-bound ferredoxin-NADP reductase. When NADP is present as the terminal electron acceptor for reduced ferredoxin, the elevated P/O value (again 1.6) is unaffected either by antimycin A or low concentrations (10 [mu]M) of heparin. When ferredoxin-catalyzed cyclic or Q-loop activity is sensitive to antimycin A, the ferredoxin pool and P-700 are both present in a largely reduced state. The opposite result is obtained for antimycin-A-insensitive activity in the presence of NADP. Our results show that conditions exist whereby ferredoxin-catalyzed cyclic electron transport is insensitive to a classical inhibitor of the cytochrome b function. We suggest that the antimycin-A-insensitive pathway of ferredoxin-catalyzed cyclic electron transport may involve the activity of ferredoxin-NADP reductase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25640/1/0000190.pd

Cyclic photophosphorylation reactions catalyzed by ferredoxin, methyl viologen and anthraquinone sulfonate. Use of photochemical reactions to optimize redox poising

The flavin analogue 5-deazariboflavin is a convenient catalyst for the photoreduction of low-potential redox compounds. In an anaerobic medium with Tricine buffer as the electron donor, 5-deazariboflavin is capable of photoreducing both ferredoxin and methyl viologen. We have used this method to conduct a comparative study of the Photosystem I photophosphorylation activities supported by the reduced forms of ferredoxin, methyl viologen and anthraquinone sulfonate. All of these catalysts are capable of generating high rates (200-500 [mu]mol ATP/h per mg chlorophyll) of cyclic photophosphorylation, but only the activity dependent on ferredoxin exhibits sensitivity to antimycin A. This finding suggests that the size of the catalyst and its ability to approach the thylakoid membrane, rather than low-redox potential, governs antimycin A sensitivity. Ferredoxin-catalyzed activity is, however, less sensitive to inhibition by dibromothymoquinone than are the activities supported by methyl viologen and anthraquinone sulfonate. This discrepancy is due to binding of the inhibitor by ferredoxin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23293/1/0000230.pd

Hydrogen peroxide oxidation catalyzed by chloride-depleted thylakoid membranes

Chloride-depleted thylakoid membranes which are unable to catalyze the oxidation of water can nonetheless catalyze the oxidation of hydrogen peroxide (Kelly, P. and Izawa, S. (1978) Biochim. Biophys. Acta 502, 198-210). Using steady-state kinetic analyses, the inhibition of hydrogen peroxide oxidation by Tris, other amines, F- has been further examined in chloride-depleted thylakoid membranes. Based on these investigations, we conclude that inhibitions of H2O2 oxidation produced by such reagents are unrelated to their inhibitory activities on the photosynthetic oxygen-evolving complex which are observed when water is the substrate (Sandusky, P.O. and Yocum, C.F. (1984) Biochim. Biophys. Acta 766, 603-611; Sandusky, P.O. and Yocum, C.F. (1986) Biochim. Biophys. Acta 849, 85-93). Experiments using the ionophore A23187 along with exogenously added Mn2+ indicate that hydrogen peroxide oxidation by chloride-depleted thylakoids is catalyzed by a pool of free or loosely bound Mn. Further, EPR measurements indicate that the presence of hydrogen peroxide, under the assay conditions employed in our experiments, release Mn from the oxygen-evolving complex in chloride-depleted membranes. It is therefore this amine-sensitive pool of loosely bound Mn that is responsible for catalysis of H2O2 photooxidation in chlrodie-depleted thylakoids.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27064/1/0000054.pd