Photosynthesis in bacteria

In 1931, comparative study of photosynthesis in bacteria led van Niel to a more general formulation of the overall reaction ... 

Early investigations of photosynthesis in bacteria and plants have led to a study of chlorins II. Quite recently the problem of biosynthesis of vitamin B12 has been shown to be connected to chlorins II, isobacteriochlorins III, and pyrrocorphins V. 

Another class of energy storage compounds consists of redox couples such as NADP+-NADPH (Table 6-1). The reduced form, NADPH, is produced by noncyclic electron flow in chloroplasts (Chapter 5, Section 5.5C). Photosynthesis in bacteria makes use of a different redox couple, NAD+-NADH. The reduced member of this latter couple also causes an... 

CBvan NIel (1929) Photosynthesis in bacteria. In Contribution to Marine Biology, pp 161-169. Stanford University... 

Despite considerable efforts very few membrane proteins have yielded crystals that diffract x-rays to high resolution. In fact, only about a dozen such proteins are currently known, among which are porins (which are outer membrane proteins from bacteria), the enzymes cytochrome c oxidase and prostaglandin synthase, and the light-harvesting complexes and photosynthetic reaction centers involved in photosynthesis. In contrast, many other membrane proteins have yielded small crystals that diffract poorly, or not at all, using conventional x-ray sources. However, using the most advanced synchrotron sources (see Chapter 18) it is now possible to determine x-ray structures from protein crystals as small as 20 pm wide which will permit more membrane protein structures to be elucidated. 

Anoxygenic photosynthesis Type of photosynthesis in green and purple bacteria in which oxygen is not produced. 

Autotrophy A unique form of metabolism foimd only in bacteria. Inorganic compounds (e.g., NH3, N02-, S2, and Fe2+) are oxidized directly (without using sunlight) to yield energy. This metabolic mode also requires energy for C02 reduction, like photosynthesis, but no lipid-mediated processes are involved. This metabolic mode has also been called chemotrophy, chemoautotrophy, or chemolithotrophy. 

Bacterial Photosynthesis A light-dependent, anaerobic mode of metabolism. Carbon dioxide is reduced to glucose, which is used for both biosynthesis and energy production. Depending on the hydrogen source used to reduce COj, both photolithotrophic and photoorganotrophic reactions exist in bacteria. 

Photocatalysis is a fundamental feature of life processes on our planet [1] (it provides photosynthesis in plants and bacteria) and of the chemistry of its atmosphere [2]. Work is under way to develop photocatalytic technologies for abatement of environmental problems [3,4]. Photocatalysis is anticipated to become in the coming years important also for selective organic synthesis [4]. In a more distant future thermal catalytic processes induced by heating with solcir radiation, together with photocatalytic processes may become important for environmentally friendly technologies of solar energy utilization [5-9]. 

Man ten, A. Phototaxis, phototropism and photosynthesis in purple bacteria and blue-green algae. Thesis, Utrecht, 1948... 

Light-driven electron transfer in plant chloroplasts during photosynthesis is accomplished by multienzyme systems in the thylakoid membrane. Our current picture of photosynthetic mechanisms is a composite, drawn from studies of plant chloroplasts and a variety of bacteria and algae. Determination of the molecular structures of bacterial photosynthetic complexes (by x-ray crystallography) has given us a much improved understanding of the molecular events in photosynthesis in general. 

The Fe-S Reaction Center (Type I Reaction Center) Photosynthesis in green sulfur bacteria involves the same three modules as in purple bacteria, but the process differs in several respects and involves additional enzymatic reactions (Fig. 19-47b). Excitation causes an electron to move from the reaction center to the cytochrome bei complex via a quinone carrier. Electron transfer through this complex powers proton transport and creates the proton-motive force used for ATP synthesis, just as in purple bacteria and in mitochondria. 

The fundamental similarity of photosynthesis in plants and bacteria, despite the differences in the electron donors they employ, becomes more obvious when the equation of photosynthesis is written in the more general form... 

Role of H2S in Some Photosynthetic Bacteria Illuminated purple sulfur bacteria carry out photosynthesis in the presence of H20 and 14C02, but only if H2S is added and 02 is absent. During the course of photosynthesis, measured by formation of [14C]carbohydrate, H2S is converted to elemental sulfur, but no 02 is evolved. What is the role of the conversion of H2S to sulfur Why is no 02 evolved ... 

The electron localized on the particle Q is subsequently used, through a complicated chain of chemical reactions, to reduce C02 to the carbohydrates (CH20)6, while the "hole localized on the particle C+ is used to oxidize some certain substrate, say hydrogen sulphide to sulphur. This results in the regeneration of the active centre C-P-J-A-Q. The overall chemical reaction of photosynthesis in purple bacteria can be thus written as... 

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