Oxygen reaction, photosynthetic

Antenna photosynthetic pigment complex that absorbs energy and transfers it to a reaction center Photosystem I reaction center from oxygen-evolving photosynthetic organisms that oxidizes plastocyanin and reduces NADP+... 

In view of the uncertainties, the search for the chemical identity of Z continued. Many similarities have been observed between the PS-II reaction center and that of the non-oxygen evolving, photosynthetic bacteria, including the homology of their amino-acid sequences and implied similarity in their three-dimensional stractures, of which that for the bacterial reaction center had been recently reported. The insights gained from such comparisons contributed immensely to the development of other new experimental approaches. 

Measurement of photosynthetic electron transport reactions Photosynthetic electron transport reactions were measured with an oxygen electrode of Rank Brothers (England). The conditions are summarized in Table 1. In order to determine optimal conditions the reduction of 2.6 dichlorophenol indophenol was measured in dependance on its pH and the KCl-conceniration. These experiments show that the maximal reaction was obtained in 30 mM tricine buffer at pH 6.5 and a KCl addition of 20 mM. 

The fundamental basis of photosynthetic carbon metabolism is the incorporation of carbon dioxide by ribulose-bisphosphate carboxylase (rubisco). This leads to the synthesis of three-carbon sugars which are either exported from the chloroplast or metabolized to regenerate the acceptor ribulose bisphosphate. Rubisco is a bifunctional enzyme in that, in parallel to carboxylation, it catalyzes an oxygenation reaction that leads to phospho-glycolate. This is the starting point for photorespiratory metabolism, which will be discussed below (Section 1.6.2). In C4 plants, the conventional C3 pattern of the photosynthetic carbon reduction Calvin cycle is confined to the bundle sheath cells. The surrounding mesophyll cells act as an ancillary carbon dioxide pump, fixing carbon dioxide via phosphoenolpyruvate carboxylase into C4 acids. These are transported to the bundle sheath for decarboxylation.In this way, photorespiration is limited because of the elevated carbon dioxide levels. 

Like the photosynthetic reaction center and bacteriorhodopsin, the bacterial ion channel also has tilted transmembrane helices, two in each of the subunits of the homotetrameric molecule that has fourfold symmetry. These transmembrane helices line the central and inner parts of the channel but do not contribute to the remarkable 10,000-fold selectivity for K+ ions over Na+ ions. This crucial property of the channel is achieved through the narrow selectivity filter that is formed by loop regions from thefour subunits and lined by main-chain carbonyl oxygen atoms, to which dehydrated K ions bind. 

The oxygen evolution rate was measured by using the photosynthetic activity measurement system (Fig. 1). When light was illuminated to the reaction vessel, algal cells began to evolve oxygen and the linearity between dissolved oxygen and time was observed just after a few... 

The oxidation of carotenes results in the formation of a diverse array of xanthophylls (Fig. 13.7). Zeaxanthin is synthesised from P-carotene by the hydroxylation of C-3 and C-3 of the P-rings via the mono-hydroxylated intermediate P-cryptoxanthin, a process requiring molecular oxygen in a mixed-function oxidase reaction. The gene encoding P-carotene hydroxylase (crtZ) has been cloned from a number of non-photosynthetic prokaryotes (reviewed by Armstrong, 1994) and from Arabidopsis (Sun et al, 1996). Zeaxanthin is converted to violaxanthin by zeaxanthin epoxidase which epoxidises both P-rings of zeaxanthin at the 5,6 positions (Fig. 13.7). The... 

As can be seen in these reactions, carotenoids may protect photosynthetic bacteria at various levels by quenching the singlet-excited state of O2 or the tiiplet-excited state of chlorophyll. The ground states of oxygen would be 3O2 and for CHL the triplet state. The carotenoids may be the preferred substrates for oxidation or may act in quenching reactive species. ... 

Photosynthesis is the reverse of reaction (30.1) the formation of carbohydrates and oxygen from water and carbon dioxide with solar energy. Photosynthesis occurs in the chloroplasts contained in the cells of green plants. The chloroplasts hold two types of photosynthetic systems, which are called PSl and PS 11. These systems... 

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