The Generation of Superoxide Radical during the Autoxidation of Hemoglobin

PGR5 Is Involved in Cyclic Electron Flow around Photosystem I and Is Essential for Photoprotection in Arabidopsis

▪ Abstract Desaturation of a fatty acid first involves the enzymatic removal of a hydrogen from a methylene group in an acyl chain, a highly energy-demanding step that requires an activated oxygen intermediate. Two types of desaturases have been identified, one soluble and the other membrane-bound, that have different consensus motifs. Database searching for these motifs reveals that these enzymes belong to two distinct multifunctional classes, each of which includes desaturases, hydroxylases, and epoxidases that act on fatty acids or other substrates. The soluble class has a consensus motif consisting of carboxylates and histidines that coordinate an active site diiron cluster. The integral membrane class contains a different consensus motif composed of histidines. Biochemical and structural similarities between the integral membrane enzymes suggest that this class also uses a diiron cluster for catalysis. Soluble and membrane enzymes have been successfully re-engineered for substrate specificity and rea...

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Desaturation and related modifications of fatty acids1

Photosynthesis provides at least two routes through which light energy can be used to generate a proton gradient across the thylakoid membrane of chloroplasts, which is subsequently used to synthesize ATP. In the first route, electrons released from water in photosystem II (PSII) are eventually transferred to NADP+ by way of photosystem I (PSI)1. This linear electron flow is driven by two photochemical reactions that function in series. The cytochrome b6f complex mediates electron transport between the two photosystems and generates the proton gradient (ΔpH). In the second route, driven solely by PSI, electrons can be recycled from either reduced ferredoxin or NADPH to plastoquinone, and subsequently to the cytochrome b6f complex2,3,4,5. Such cyclic flow generates ΔpH and thus ATP without the accumulation of reduced species. Whereas linear flow from water to NADP+ is commonly used to explain the function of the light-dependent reactions of photosynthesis, the role of cyclic flow is less clear. In higher plants cyclic flow consists of two partially redundant pathways. Here we have constructed mutants in Arabidopsis thaliana in which both PSI cyclic pathways are impaired, and present evidence that cyclic flow is essential for efficient photosynthesis.

Cyclic electron flow around photosystem I is essential for photosynthesis

The structure and mechanism of iron-hydrogenases

Ferredoxins as Electron Carriers in Photosynthesis and in the Biological Production and Consumption of Hydrogen Gas

Ferredoxins as electron carriers in photosynthesis and in the biological production and consumption of hydrogen gas.

Oxidation-reduction potentials and stoichiometry of electron transfer in ferredoxins.

limited number of mutually specific cohesive sites implied thereby suggests a specialized biological function, one that remains to be identified. Summary.-The DNA of phage lambda undergoes reversible transitions from linear to characteristically folded molecules, and from linear monomers to open polymers. Some conditions favoring one state or another have been defined. It may be surmised that each molecule carries two specifically interacting cohesive sites.

https://www.pnas.org/content/pnas/49/4/567.full.pdf

Role of Chloroplast Ferredoxin in the Energy Conversion Process of Photosynthesis

Photoproduction of Hydrogen, Photofixation of Nitrogen and a Unified Concept of Photosynthesis

K. Tagawa

Papers

Ferredoxins as electron carriers in photosynthesis and in the biological production and consumption of hydrogen gas.

Oxidation-reduction potentials and stoichiometry of electron transfer in ferredoxins.

Role of Chloroplast Ferredoxin in the Energy Conversion Process of Photosynthesis

Photoproduction of Hydrogen, Photofixation of Nitrogen and a Unified Concept of Photosynthesis

Separation of the light and dark reactions in electron transfer during photosynthesis