Iron-sulfiir clusters

Phillips, J. D., Graham, L. A., and Trumpower, B. L., 1993, Subunit 9 of the Saccharomyces cere-visiae cytochrome bci complex is required for insertion of EPR-detectable iron-sulfiir cluster into the Rieske iron-sulfiir protein, J. Biol. Chem. 268 11727nl 1736. 

Nitric oxide is not in itself very reactive or particularly toxic. However, its interaction with other oxidants may yield products whose toxicity may result of significance. Such is the case of peroxynitrite (ONOO ) which is formed in a non-enzymatic reaction between NO and O2-. This reaction follows a 1 1 stoichiometry and it has a very fast reaction speed (6.7 X 10 mol/L s [40] which is 3 times higher than the capacity of O2 dismutation by SOD and around 1000 times greater than the reaction of NO with iron-sulfiir clusters [41 ]. 

Numerous cellular enzymes and coenzymes require iron, either as an integral part of the molecule or as a cofactor. Notable are the peroxidases and cytochromes, all of which, like Hb, are heme proteins. Other enzymes, such as aconitase and ferredoxin, have iron that is coordinated with sulfur in a so-called iron-sulfiir cluster. Nearly half of the enzymes of the Krehs cycle contain iron. These enzymes and coenzymes, which appear in aU nucleated cells of the body, are referred to collectively as the tissue iron compartment. The tissue iron compartment normally amounts to approximately 8 mg. Although a small compartment, it is metabolicaUy critical. Some iron enzyme activities dimmish early in the course of iron deficiency. ... 

Naphthalene dioxygenase consists of three components, which form an electron transfer chain an NADH-dependent flavoprotein reductase, a ferredoxin containing two [2Fe2S] Rieske iron-sulfur clusters, and a Rieske oxygenase containing both a [2Fe2S] Rieske iron-sulfiir cluster and a mononuclear iron(II) center in the enzyme active site. ° ... 

The chromium(II)-edta system is powerfully reducing (the half-wave potential is -1.48 V at pH 12 vs. SCE) and has been used in the reduction of iron-sulfiir clusters. No solid complex has been isolated because of its instability to oxidation, but Cr -edta is high-spin in aqueous solution (fieff = 5.12 BM) and its stability constant has been determined. The edta is believed to be pentadentate with H2O in the sixth position. ... 

Nanosecond Spectroscopy of Early Electron Transfers in Photosystem 1. Iron-Sulfiir Cluster Fx is Reduced within 5 Nanoseconds 635... 

The enzyme is simpler than the other, iron-sulfiir cluster-containing hydro-genases discussed below. It shows no sequence homology with any other hydrogenase, or any other protein. It does not catalyze the reduction of electron acceptors, or the exchange of D2 with H2O, except in the presence of its cofactor, methyleneH4MPT. This is an extraordinary and vmprecedented reaction, the direct transfer of hydride from H2 to a carbon atom. The enzyme is extremely active, but very sensitive to O2 and light. 

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