Electron transport iron-containing proteins

QH2 participates in a chain of redox reactions with electron-transporting iron-containing proteins called cytochromes (Real Life 8-1). The reduction of Fe to Fe in cytochrome b by QH2 begins a sequence of electron transfers involving six different proteins. The chain ends with reduction of O2 to water by addition of four electrons and four protons. 

Calcium-binding Proteins Copper Enzymes in Denitrification Copper Proteins with Type 1 Sites Copper Proteins with Type 2 Sites Iron Heme Proteins Electron Transport Iron-Sulfin Proteins Metal-mediated Protein Modification Metallochaperones Metal Ion Homeostasis Molybdenum MPT-containing Enzymes Nickel Enzymes Cofactors, Nitrogenase Catalysis Assembly Zinc Enzymes. 

Chapter 7 has reported on the importance of iron in biological species. Because iron is the most abundant transition metal found in biological species, one would expect a wide variety of iron-containing proteins and metalloenzymes. Only a few of these have been treated in any detail in this chapter. Little or no mention has been made of how or why iron ions evolved to be the most biologically abundant transition metal ions probably their usefulness in redox situations and for electron transport has something to do with their popularity. Iron homeostasis in biological species has not been discussed, although this... 

The second class of iron-containing proteins which have been well-studied by Mossbauer spectroscopy, and by other resonance techniques, are the iron-sulfur proteins. These molecules are also known by the name, ferredoxins. Iron-sulfur proteins in several varieties serve as electron-transport agents for processes in plants, bacteria, and mammals. Perhaps the most-studied physiological process involving the iron-sulfur proteins is the study of their role in photosynthesis. This subject has been extensively reviewed by Arnon 126,135), Hind and Olson 127), Hall and... 

The association of proton movement with electron transport is not reflected in the fatty acyl desaturase system universal to endomembranes. In these enzymes the dehydrogenase, NADH cyt b5 reductase and the cytochrome b5 (a single heme cytochrome) are associated exclusively with the cytosolic side of the membrane by acyl groups and have no transmembrane segment. The cytochrome b5 oxidase associated with the desaturation of fatty acyl CoA may be transmembranous but has not been associated with proton movement. It is an iron-containing protein. The other type of endomembrane cytochromes are the P-450 group of cytochrome bs... 

The electron-transport chain contains a number of iron-sulfur proteins (also known as nonheme iron proteins). The iron atoms are bound to the proteins via cysteine —S— groups and sulfide ions one such 4-Fe cluster is shown in Fig. 14-1. These proteins mediate electron transport by direct electron transfer changes in oxidation state of the iron in iron-sulfur proteins can be monitored by electron spin resonance spectroscopy (ESR). 

Fe3+ in iron-sulfur proteins has an electron spin resonance (esr) signal, while Fe2+ does not. Assume that you have a preparation of mitochondria that are able to synthesize ATP via oxidation of NADH supplies of rotenone, antimycin A, and KCN and access to an esr spectrometer. How could you establish which of the complexes of the electron-transport chain contain iron-sulfur proteins ... 

Cobalt B Enzymes Coenzymes Cytochrome Oxidase Iron Heme Proteins Electron Transport Iron Proteins with Dinuclear Active Sites Iron Proteins with Mononuclear Active Sites Iron-Sulfur Models of Protein Active Sites Metallocenter Biosynthesis Assembly. Metalloregulation Molybdenum MPT-containing Enzymes Nickel Enzymes Cofactors Nitrogenase Catalysis Assembly Photosynthesis Tungsten Proteins Vanadium in Biology Zinc DNA-binding Proteins. 

Most known multiheme cytochromes and enzymes belong to the family of cytochromes c (see Iron Heme Proteins Electron Transport), which contain Fe-protoporphyrin IX covalently attached to the polypeptide chain by two thioether bonds, formed by addition of two cysteinyl residues to the vinyl side-chains of the porphyrin ring. The two cysteines form a characteristic amino acid sequence motif CXXCH, usually indicative of heme c ligation, and where the histidine is the axial fifth ligand to the iron. For some cytochromes (see Section 2), the number of residues between the two cysteines can be three or four. The heme redox potentials in cytochromes c cover a wide range and are tuned by several factors, usually dominated by the type of axial ligation and the extent of solvent exposure of the heme. ... 

The following material focuses on fte reduction of oxygen to water and ATP production, events that take place at the mitochondrial membrane. Energy fuels are electron donors. The coenz)anes NAD" and FAD accept these electrons and mediate their transfer to the respiratory chain. The respiratory chain is a series of iron-containing proteins associated with the mitochondrial membrane. Transfer of four electrons through this series of proteins can result in the reduction of one molecule of oxygen to water. This electron transport chain is shown in Figure 5.2. 

Iron-containing proteins are essential for photosynthetic and respiratory electron transport. Chlorophyll synthesis is also dependent on iron, and chlorophyll content is diminished under iron limitation. Requirements for iron are also influenced by the nitrogen substrate used to support growth. Both nitrate and nitrite reductases contain iron in their catalytical centres. Iron efficiency models (Raven, 1988) and culture studies (Maldonado Price, 1999) show that cells using nitrate require 60-70% more cellular iron to support a given growth rate than those assimilating ammonia. 

Iron is by far the most widespread and important transition metal with a functional role in living systems. Iron-containing proteins participate in two main processes oxygen-transport and electron-transfer. There are then other molecules whose function is to store and transport iron itself. 

Although iron deficiency anemia is characterized by decreased levels of hemoglobin and other iron-containing proteins in the blood, the iron-containing cytochromes and Fe-S centers of the electron transport chain in tissues such as skeletal muscle are affected as rapidly. Fatigue in iron deficiency anemia, in patients such as Ann O Rexia (see Chapter 16), results, in part, from the lack of electron transport for ATP production. 

What is the nature of the iron-containing proteins of electron transport ... 

The electron transport chain consists of four multisubunit membrane-bound complexes and two mobile electron carriers (coenzyme Q and cytochrome c). The reactions that take place in three of these complexes generate enough energy to drive the phosphorylation of ADP to ATP. Many proteins of the electron transport chain contain iron, either as part of a heme or combined with sulfur. 

What is the nature of the iron-containing proteins of eiectron transport A number of iron-containing proteins are part of the electron transport chain. In the cytochrome proteins, the iron is bound to a heme group. In other proteins, the iron is bound to the protein along with sulfur. 

Ferredoxins, Fat low-molecular- mass iron-sulfur proteins which transfer electrons from one enzyme system to another, without possessing any enzyme activity themselves. The name was coined by Mortenson for iron-containing proteins from Clostridium pasteu-ranum. The 8-Fe-Fd take part in many election transport processes in organisms like Clostridia and photosynthetic bacteria (Table). The primary structures of many of these proteins have been determined. They consist of about SS amino adds, including 8 cysteines, which occupy the same positions in each Fd. The molecule contains two identical 4Fe-4S clusters, each one forming a cube and covalently bonded to 4 cysteine residues in the peptide chain. Each 4Fe-4S center can transfer one electron. 

When induced in macrophages, iNOS produces large amounts of NO which represents a major cytotoxic principle of those cells. Due to its affinity to protein-bound iron, NO can inhibit a number of key enzymes that contain iron in their catalytic centers. These include ribonucleotide reductase (rate-limiting in DNA replication), iron-sulfur cluster-dependent enzymes (complex I and II) involved in mitochondrial electron transport and cis-aconitase in the citric acid cycle. In addition, higher concentrations of NO,... 

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