Light-independent process

L-/D-cvsteine. Hydrogen sulfide is produced from L-cysteine in a light-independent process that can be inhibited in vivo and in vitro by aminooxy acetic acid, an inhibitor of pyridoxal phosphate-dependent enzymes the hydrogen sulfide emitted in response to L-cysteine is directly derived from die L-cysteine fed ( 2 ). Therefore, hydrogen sulfide appears to be produced from L-cysteine by a pyridoxal phosphate-dependent, L-cysteine specific cysteine desulfhydrase. This conclusion is supported by the finding that in cucurbit... 

This reaction is possible because the H /H2 redox system (E g -0.42V) is a more powerful reducing system than the NAD /NADH redox system (E n -0.32V) and is exergonic to the extent of 19.3 kj mol" under standard conditions. Thus NADH generation in Chromatium growing on Hj is a light-independent process however light is required to drive c-p/p and generate the ATP that is required, in addition to NADH, for CO2 fixation. 

The light independent reactions take place in the stroma with the help of ATP and NADPH. In a process called the Calvin-Benson cycle, or carbon fixation, carbon dioxide from the atmosphere is captured and converted into carbohydrates [135]. The reaction is catalyzed by the enzyme RuBisCO (ribulose-1,5-biphosphate... 

Somatic hypermutation has been studied in detail in mice and humans, but no doubt operates in a similar fashion in a variety of other species, modifying the repertoire that is initially established by V(D)J recombination before the introduction of antigen. In the case of V regions of K light chains in sheep, somatic hypermutation also contributes toward the generation of the preimmune repertoire in an antigen-independent process (Reynaud et al., 1991, 1995). 

Nevertheless, some properties of these resonances can be deduced from the general considerations. In particular, in the low light-power limit, the optical rotation amplitudes of the hexadecapole resonances are obviously proportional to the square of the light intensity I2, as they are induced by the four-photon atomic coherence. The corresponding signals scale as I4, as observed experimentally (Fig. 11). Moreover, the light-independent relaxation rate for hexadecapole resonances must be large as compared to 7, if the relaxation of atomic polarization is conditioned by the processes which are different for the PM of different rank k. As we have seen above, this expectation is confirmed experimentally. 

The incorporation of COz into carbohydrate by eukaryotic photosynthesizing organisms, a process that occurs within chloroplast stroma, is often referred to as the Calvin cycle. Because the reactions of the Calvin cycle can occur without light if sufficient ATP and NADPH are supplied, they have often been called the dark reactions. The name dark reactions is somewhat misleading, however. The Calvin cycle reactions typically occur only when the plant is illuminated, because ATP and NADPH are produced by the light reactions. Therefore light-independent reactions is a more appropriate term. Because of the types of reactions that occur in the Calvin cycle, it is also referred to as the reductive pentose phosphate cycle (RPP cycle) and the photo synthetic carbon reduction cycle (PCR cycle). 

The Calvin cycle is a series of light-independent reactions in which C02 is incorporated into organic molecules. The Calvin cycle reactions occur in three phases carbon fixation, reduction, and regeneration. Photorespiration is a wasteful process in which photosynthesizing cells evolve C02. 

The Z scheme is a mechanism whereby electrons are transferred from water to NADP +. This process produces the reducing agent NADPH required for fixing carbon dioxide in the light-independent reactions of photosynthesis. Removal of the electrons from water also results in the production of oxygen. As electrons flow from PSII to PSI, protons are... 

Light-induced processes are described quite differently in molecular photochemistry and solid-state photophysics. In photochemistry one is used to an atomistic picture in which the arrangement of the atoms in the structure of a single molecule determines the electronic levels and thus the photochemical behavior. In contrast, the electronic levels of a solid are determined by the infinite periodicity of the atomic sequence in the crystal lattice. This leads to a basic concept according to which the solid can be treated as a dielectric continuum. Atomistic irregularities in the crystalline structure, such as lattice defects or impurities, are treated as perturbations of the spatially independent states in the energy bands. 

With very few exceptions, life directly or indirecdy depends on photosynthesis. The electric current is the flow of electrons from water to NADP+ a light-requiring process. The current continues in the light-independent reactions, with electrons flowing from NADPH to 6 phosphoglycerate, which ultimately yields glucose. 

The mechanism of action of coumarins are too complex and far fi-om being completely understood. However, they generally can be divided into two light-dependent and independent processes. Since there are already many reports on the light-dependent action of coumarins and furanocoumarins [10,241,269,270,271,272,273] that can explain their antifungal activity, here we try to focus on the light-independent mechanisms. 

In the light-independent or dark reactions the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase oxygenase) consumes CO2 from the atmosphere and in a complex process called the Calvin-Benson cycle releases three-carbon sugars that are subsequently combined to form glucose. 

In addition to direct emission in combustion processes, most secondary formation pathways in the gas and aqueous phases depends on ozone. By contrast, there is only one way that is light independent (ozonolysis) and another way that is independent of oxidant precursors (aqueous phase electron transfer onto oxygen Eqs. 5.96 and 5.102). 

In 1924, the mystery of how sunlight could prevent rickets was partially solved. Dr. Harry Steenbock of the University of Wisconsin and Dr. A. Hess of Columbia University, working independently, showed that the antirachitic activity could be produced in foods and in animals by ultraviolet light. The process, known as the Steenbock Irradiation Process was patented by Steenbock, with the royalties assigned to the Wisconsin Alumni Research Foundation of the University of Wisconsin. Subsequent research disclosed that it was certain sterols in foods and animal tissues that acquired antirachitic activity upon being irradiated. Before irradiation, the sterols were not protective against rickets. 

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