Cytochromes nitrogen fixation

Many key protein ET processes have become accessible to theoretical analysis recently because of high-resolution x-ray stmctural data. These proteins include the bacterial photosynthetic reaction centre [18], nitrogenase (responsible for nitrogen fixation), and cytochrome c oxidase (the tenninal ET protein in mammals) [19, 20]. Although much is understood about ET in these molecular machines, considerable debate persists about details of the molecular transfonnations. 

The many redox reactions that take place within a cell make use of metalloproteins with a wide range of electron transfer potentials. To name just a few of their functions, these proteins play key roles in respiration, photosynthesis, and nitrogen fixation. Some of them simply shuttle electrons to or from enzymes that require electron transfer as part of their catalytic activity. In many other cases, a complex enzyme may incorporate its own electron transfer centers. There are three general categories of transition metal redox centers cytochromes, blue copper proteins, and iron-sulfur proteins. 

Fe Cytochrome oxidase reduction of oxygen to water Cytochrome P-450 0-insertion from O2, and detoxification Cytochromes b and c electron transport in respiration and photosynthesis Cytochrome f photosynthetic electron transport Ferredoxin electron transport in photosynthesis and nitrogen fixation Iron-sulfur proteins electron transport in respiration and photosynthesis Nitrate and nitrite reductases reduction to ammonium... 

Cytochrome c peroxidase, 70S Cytochromes, 618 bacteria, 622 classification, 619 horse heart, 620 nitrogen fixation. 728 redox potential, 616 axial ligands, 617 respiration, 624... 

It has recently become apparent that iron-sulphur, or non-haem iron, proteins occur widely in animals, plants, and bacteria, and that they play a very important role in such functions as respiration, photosynthesis, and nitrogen-fixation. Both iron-sulphur proteins and cytochromes are electron carriers containing iron, but their active centres are entirely different. Hall and Evans have recently reviewed iron-sulphur proteins, and a discussion on nitrogen fixation held in June 1968 has also been published. ... 

O2 carriers), ferredoxins and cytochromes (redox processes), ferritin (iron storage), acid phosphatase (hydrolysis of phosphates), superoxide dismutases (O2 dismuta-tion) and nitrogenase (nitrogen fixation). A deficiency of iron in the body causes anaemia (see Box 21.6), while an excess causes haemochromatosis. 

Anabaena cylindrica sp. PCC7I20 [NiFe] hydrogenase Putative membrane- bound cytochrome b reducing H2 recycling during N2 fixation O2, nitrogen limitation, heterocyst formation 2... 

Iron, like many of the micronutrients, is involved in enzymatic reactions. It is a constituent of cytochrome respiratory pigments found in animals, higher plants and microorganisms. These pigments that are involved in intracellular oxidations, are chemically much like hemoglobin, since they are complexes of iron, porphyrin and a protein. Cytochrome-c and the iron-porphyrin enzyme, cytochrome oxidase, both take part in cell respiration (Hewitt, 1951), and are probably also involved in photosynthesis. Iron is also required for fixation of elemental nitrogen in free-living and nodule bacteria (Nicholas, 1961). 

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