Light reaction

Photosynthesis Consists of Both Light Reactions and Dark Reactions... 

FIGURE 22.4 The light-dependent and light-independent reactions of photosynthesis. Light reactions are associated with the thylakoid membranes, and light-independent reactions are associated with the stroma. 

Most of the enzymes mediating the reactions of the Calvin cycle also participate in either glycolysis (Chapter 19) or the pentose phosphate pathway (Chapter 23). The aim of the Calvin scheme is to account for hexose formation from 3-phosphoglycerate. In the course of this metabolic sequence, the NADPH and ATP produced in the light reactions are consumed, as indicated earlier in Equation (22.3). 

Gates, B. J., and DeLuca, M. (1975). The production of oxyluciferin during the firefly luciferase light reaction. Arch. Biochem. Biophys. 169 616-621. 

Homolytic scission of the 0-0 bond of hydrogen peroxide may be effected by heat or UV irradiation.245 The thermal reaction requires relatively high temperatures (>90 Photolytic initiation generally employs 254 nm light. Reactions in organic media require a polar cosolvent (e.g. an alcohol). 

IRON-SULFUR CENTERS INVOLVED IN PHOTOSYNTHETIC LIGHT REACTIONS... 

The 2[4Fe-4S] and [3Fe-4S][4Fe-4S] ferredoxins are components of virtually all eubacteria and archaebacteria (3). Several comprehensive reviews dealing with these small metalloproteins have appeared (3, 8-12), but only those participating directly in the photosynthetic light reactions will be addressed here. 

IRON-SULFUR CENTERS IN PHOTOSYNTHETIC LIGHT REACTIONS 341... 

Small semiconductor particles also act like microelectrodes upon illumination. Electrons and positive holes are created in the particles which initiate redox reactions. The charge carriers may also recombine and emit fluorescence light. Reaction with a solute leads to quenching of the fluorescence. 

Figure 12.2b. Scheme for three light reactions in plant photosynthesis proposed by Knaff and Amon.(39)... 

NHS-fluorescein is insoluble directly in aqueous solution and should be dissolved in organic solvent prior to addition of a small aliquot to a buffered reaction medium. Concentrated stock solutions may be prepared in DMSO or DMF. Such solutions are relatively stable if protected from light. Reaction conditions should be maintained at the optimal reactivity for NHS esters—pH 7-9. 

Light reaction. This is a photochemical phase and takes place in the thylakoid membrane of the chloroplast, where light energy is converted to chemical energy. 

Dark reaction. This is a biosynthetic phase that takes place in the stroma within the chloroplasts converting C02 to sugar. This process does not require light, but requires the products of the light reaction namely ATP and NADPH, which are... 

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