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Carbon, Nitrogen, and Sulfur Chemistry
Published in Jerome Greyson, Carbon, Nitrogen, and Sulfur Pollutants and Their Determination in Air and Water, 2020
“Symbiotic” fixation involves bacterial infection of the root cells of the host plant. The bacteria then multiply in nodules attached to the plant roots. Stimulated by the plant, the bacteria produce an enzyme called nitrogenase, which catalyzes the conversion of atmospheric nitrogen to ammonia. The actual mechanisms involved in the conversion are not well understood, although it seems that nitrogenase behaves like a hydrogenase, an enzyme that can catalyze reduction reactions involving molecular hydrogen. It has also been observed that some nitrogen fixing bacteria produce an iron-containing protein called ferredoxin,† a strong reducing agent that is apparently necessary to the bacterium’s ability to fix nitrogen. And, finally, it is known that ATP is consumed in the process. Thus, it appears that fixation may involve the reduction of hydrogen ions to moleular hydrogen, which then reacts with atmospheric nitrogen to form ammonia, all catalyzed by nitrogenase, and with the ATP providing the energy requirements to drivethe reactions. It has been estimated that fixation of one mole of nitrogen by Rhizobium requires 25 to 30 ATP molecules [Alberts et al 1983, 1117].
Turfgrass Physiology and Environmental Stresses
Published in L.B. (Bert) McCarty, Golf Turf Management, 2018
Components of the light reactions (also called the electron transport system or “Z” scheme; Figure 2.20) are designated photosystem I (PSI) and photosystem II (PSII). These photosystems can be considered as light-driven electron pumps that work in two different, but overlapping, areas. PSII absorbs light in the red region (around 680 nm), while PSI absorbs light in the far-red region (around 700 nm). The PSII contains a different chlorophyll, designated P680, as well as chlorophyll a (chl a) antenna and carotenoids. The PSI complex contains the following pigments: a special chl a or P700 in the reaction center; chl a antenna; and the carotenoids β-carotene and xanthophyll. Photosystem II and PSI are arranged sequentially in the electron transport chain to transfer energy from H2O to NADP+ (Figure 2.20). Electron transport involves several carrier molecules connecting the two photosystems. The electrons are finally passed to ferredoxin (Fd), a water-soluble iron-sulfur protein found on the stromal side of the thylakoid membrane. Ferredoxin donates the electron to NADP+, reducing it to NADPH.
Microorganisms and Their Role in Soil
Published in Subhas K. Sikdar, Robert L. Irvine, Fundamentals and Applications, 2017
Ludwig Davids, Hans-Curt Flemming, Peter A. Wilderer
The reducing power needed for dinitrogen reduction is in the form of reduced ferredoxin and, in heterotrophs, may come from a reaction in which pyruvate is oxidatively decarboxylated. In phototrophs, the reduced ferredoxin is produced as part of the photophosphorylation mechanism. Nitrogen fixation is a very energy-intensive reaction that consumes as many as 16 moles of ATP per mole of dinitrogen becoming reduced to ammonia (Newton and Burgess, 1983). Nitrogen fixation may proceed symbiotically or nonsymbiotically. Symbiotic nitrogen fixation requires that the nitrogen-fixing bacterium associates with a specific plant, e.g., legumes, several nonleguminous angiosperms, the water fern Azolla, fungi (certain lichens), or in rare cases, with an animal host in order to carry out nitrogen fixation. In nonsymbiotic nitrogen fixation, the active organisms are free-living in soil or water and fix nitrogen if fixed nitrogen is limiting. Their nitrogenase is not distinctly different from that of symbiotic nitrogen fixers. The capacity for nonsymbiotic nitrogen fixation is widespread among procaryotes. For a more detailed discussion of nitrogen fixation, the reader is referred to Alexander (1984).
Theory of chemical bonds in metalloenzymes XXIV electronic and spin structures of FeMoco and Fe-S clusters by classical and quantum computing
Published in Molecular Physics, 2020
Koichi Miyagawa, Mitsuo Shoji, Hiroshi Isobe, Shusuke Yamanaka, Takashi Kawakami, Mitsutaka Okumura, Kizashi Yamaguchi
The UB3LYP calculations were performed for the low-spin (LS) 1D collinear BS solution with the mixed-valence configuration, Fe(III) ↑ Fe(III) ↑ Fe(III) ↓ Fe(II) ↓ (S=(5 + 5-5-4)/2 = 1/2) and the high-spin (HS) configuration Fe(III) ↑ Fe(III) ↑ Fe(III) ↑ Fe(II) ↑. The 4Fe-4S clusters (7, 8, and 9) have the cubane-type skeletons as shown in Figure 1 and the Fe centres are further coordinated by cysteine ligands [1–6]. The Fe4S4 electron transfer proteins are usually subdivided into low- and high (HiPIP)-potential ferredoxins. We have examined the HiPIP Fe4S4 cluster [12,13], [Fe(II)Fe(III)3(SCH3)4] (7a), with the hydrogen bonding, where all the cysteine ligands are modelled as –SCH3. Amido bonds contributing to H-bonds in a main chain are substituted for CH3-NHCO-H as illustrated in Figure 15(B). The BS (AF) solution for the low-spin state (S=1/2) was constructed by the spin flipping procedure for the highest spin state (S=19/2) for 7a [61]. The UB3LYP/MIDI [88,89] calculations were performed for 7a with S=1/2 to elucidate the importance of environmental effects.
Effect of different kinds of complex iron on the growth of Anabaena flos-aquae
Published in Environmental Technology, 2019
Yongting Qiu, Zhihong Wang, Feng Liu, Junxia Liu, Tao Zhou
Prior studies have showed that nitrogen and phosphorus in natural water were the major nutrition elements to affect the growth of microorganisms and the structure of the community [6,7]. However, much attention has been paid to how micro-metallic elements (Iron, Copper, Zinc, etc.) affected the microbial growth. Of these elements, iron plays an important role in the growth and physiological processes of microalgae [8]. Iron can co-ordinate active oxygen and take part in electron transporting, enzymatic reactions, photosynthesis and respiration, and the synthesis of proteins and nucleic acids [9,10]. Ferritin is an indispensable protein in photosynthesis and respiration, which directly participates in a series of biosynthesis and biodegradation, such as the reduction of nitrate and nitrite, nitrogen fixation and the synthesis of chlorophyll [11]. In addition, iron can take part in oxygen circulation as a composition of catalase, peroxidase and superoxide dismutase. Ferredoxin can be electron donors of the process of sulphate reduction, nitrate reduction and nitrogen fixation. Iron catalysts impacts on the cell metabolism by regulating the activity of enzyme [12].