Photosynthetic phosphorylation

Photosynthetic phosphorylation of protein side chains 79 substrate level 775, 800 Phosphorylation, photosynthetic. See Photosynthetic phosphorylation Phosphorylation reactions 303 Phosphorylation state ratio definition of 303 O-Phosphoserine 610s Phosphoserine 545 Phosphothreonine 545 Phosphotransferase system bacterial 419,420 Phosphotransferases 637... 

ADENOSINE DI-AND TRIPHOSPHATE. See Carbohydrates Phosphorylation (Oxidative) Phosphorylation (Photosynthetic). 

Peter Mitchell (Nobel Prize, 1978) of Great Britain was the first to realize, and to propose in his chemi-osmotic theory, that the energy required for die ADP-ATP reaction could be derived by an accretion of protons in the thylakoid sac to the point at which the electrochemical gradient across the membrane could effect the proton transport required as die driving force for this reaction. See also Phosphorylation (Photosynthetic). 

Photosynthetic Eiectron Transport Diverted Mitochondriai Eiectron Transport Oxidative Phosphorylation Photosynthetic Electron Transport (Hill Reaction) Carbon Metabolism -. n .n.ii... 

Nerve axon Thylakoid Visual receptor Mitochondria Chloroplast Ribosomes Conduction of nerve impulse Conversion of light into energy Conversion of light into chemical energy Oxidative phosphorylation Photosynthetic phosphorylation Protein synthesis... 

The energy produced on hydrolysis of ATP is utilised in many biological processes. These include muscle contraction, the transport of ions and molecules across cell membranes and the synthesis of various biomolecules. The biosynthesis of ATP is mainly by oxidative phosphorylation, photosynthetic phosphorylation and substrate-level phosphorylation (Chapter 11.5). In 1941, Lipmann introduced the concept of high-energy phosphate bonds and indicated that ATP was the universal energy carrier in bio systems. 

The importance of quinones with unsaturated side chains in respiratory, photosynthetic, blood-clotting, and oxidative phosphorylation processes has stimulated much research in synthetic methods. The important alkyl- or polyisoprenyltin reagents, eg, (71) or (72), illustrate significant conversions of 2,3-dimethoxy-5-methyl-l,4-ben2oquinone [605-94-7] (73) to 75% (74) [727-81-1] and 94% (75) [4370-61-0] (71—73). 

The quantum yield of photosynthesis, the amount of product formed per equivalent of light input, has traditionally been expressed as the ratio of COg fixed or Og evolved per quantum absorbed. At each reaction center, one photon or quantum yields one electron. Interestingly, an overall stoichiometry of one translocated into the thylakoid vesicle for each photon has also been observed. Two photons per center would allow a pair of electrons to flow from HgO to NADP (Figure 22.12), resulting in the formation of 1 NADPH and Og. If one ATP were formed for every 3 H translocated during photosynthetic electron transport, 1 ATP would be synthesized. More appropriately, 4 hv per center (8 quanta total) would drive the evolution of 1 Og, the reduction of 2 NADP, and the phosphorylation of 2 ATP. 

The thylakoid membrane is asymmetrically organized, or sided, like the mitochondrial membrane. It also shares the property of being a barrier to the passive diffusion of H ions. Photosynthetic electron transport thus establishes an electrochemical gradient, or proton-motive force, across the thylakoid membrane with the interior, or lumen, side accumulating H ions relative to the stroma of the chloroplast. Like oxidative phosphorylation, the mechanism of photophosphorylation is chemiosmotic. 

Phototactic action spectra of Phormidium autumnale and Phormidium uncinatum, measured by Nultsch86>89), show prominent maxima in the absorption range of C-phycoerythrin and smaller, but distinct, peaks in the absorption range of C-phyco-cyanin. Red light absorbed by chlorophyll a is not active, while in the blue range absorbedby the Soret band, the action spectrum shows aminimum(Fig. 6). Nultsch87) concluded that biliproteins are photoreceptors of phototaxis, but independently of the photosynthetic electron transport and phosphorylation. 

Mitchell, P. (1966). Chemiosmotic Coupling in Oxidative and Photosynthetic Phosphorylation. Glynn Research, Bodmin, Cornwall, U.K. 

Photosynthetic prokaryotes do not have chloroplasts. Their photosynthetic pigments are embedded in their cell walls. Some use bacteriochlorophyll for light harvesting. In the proteobacteria and archaea, light harvesting is accomplished by the protein rhodopsin, which acts as a photo-driven proton pump that fuels phosphorylation of ADP. 

Both the time of analysis and experimental design may affect the results. An explanation for the increase in adenylates under the conditions of our experiment is still needed. Since both ATP alone and total adenylate concentrations have increased, it does not appear that a shift in phosphorylation can account for the increases. The decrease in photosynthesis and increase in adenylates occur during the same time period and both factors return to normal after 21 hr. From previous research we know that the photosynthetic levels of ozonated pinto bean foliage decrease immediately after ozone exposure even when symptoms do not develop ( ). This does not hold true for the adenylate or respiration responses. Therefore, it appears that the ozone-initiated increase in adenylates is not correlated directly to the photosynthetic response. The increase in respiration persists when adenylate content and photosynthetic rates have returned to normal. Impaired mitochondrial function appears to be a secondary response more closely related to symptom development. 

ATP is the primary high-energy phosphate compound produced by catabolism, in the processes of glycolysis, oxidative phosphorylation, and, in photosynthetic cells, photophosphorylation. Several enzymes then cany phosphoryl groups from ATP to the other nucleotides. Nucleoside diphosphate kinase, found in all cells, catalyzes the reaction... 

The transfer of phosphoryl groups is a central feature of metabolism. Equally important is another kind of transfer, electron transfer in oxidation-reduction reactions. These reactions involve the loss of electrons by one chemical species, which is thereby oxidized, and the gain of electrons by another, which is reduced. The flow of electrons in oxidation-reduction reactions is responsible, directly or indirectly, for all work done by living organisms. In nonphotosynthetic organisms, the sources of electrons are reduced compounds (foods) in photosynthetic organisms, the initial electron donor is a chemical species excited by the absorption of light. The path of electron flow in metabolism is complex. Electrons move from various metabolic intermediates to specialized electron carriers in enzyme-catalyzed reactions. 

FIGURE 20-27 Regulation of sucrose phosphate synthase by phosphorylation. A protein kinase (SPS kinase) specific for sucrose phosphate synthase (SPS) phosphorylates a Ser residue in SPS, inactivating it a specific phosphatase (SPS phosphatase) reverses this inhibition. The kinase is inhibited allosterically by glucose 6-phosphate, which also activates SPS allosterically. The phosphatase is inhibited by Pi, which also inhibits SPS directly. Thus when the concentration of glucose 6-phosphate is high as a result of active photosynthesis, SPS is activated and produces sucrose phosphate. A high P, concentration, which occurs when photosynthetic conversion of ADP to ATP is slow, inhibits sucrose phosphate synthesis. 

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