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Redox Reactions of NO and O<sub>2</sub> in Iron Enzymes : A Density Functional Theory Study

<p>In the present thesis the density functional B3LYP has been used to study reactions of NO and O<sub>2</sub> in redox active enzymes.</p><p>Reduction of nitric oxide (NO) to nitrous oxide (N<sub>2</sub>O) is an important part in the bacterial energy conservation (denitrification). The reduction of NO in three different bimetallic active sites leads to the formation of hyponitrous acid anhydride (N<sub>2</sub>O<sub>2</sub><sup>2-</sup>). The stability of this intermediate is crucial for the reaction rate. In the two diiron systems, respiratory and scavenging types of NOR, it is possible to cleave the N-O bond, forming N<sub>2</sub>O, without any extra protons or electrons. In a heme-copper oxidase, on the other hand, both a proton and an electron are needed to form N<sub>2</sub>O.</p><p>In addition to being an intermediate in the denitrification, NO is a toxic agent. Myoglobin in the oxy-form reacts with NO forming nitrate (NO<sub>3</sub> <sup>-</sup>) at a high rate, which should make this enzyme an efficient NO scavenger. Peroxynitrite (ONOO<sup>-</sup>) is formed as a short-lived intermediate and isomerizes to nitrate through a radical reaction.</p><p>In the mechanism for pumping protons in cytochrome oxidase, thermodynamics, rather than structural changes, might guide protons to the heme propionate for further translocation.</p><p>The dioxygenation of arachidonic acid in prostaglandin endoperoxide H synthase forms the bicyclic prostaglandin G<sub>2</sub>, through a cascade of radical reactions. The mechanism proposed by Hamberg and Samuelsson is energetically feasible.</p>

Identiferoai:union.ndltd.org:UPSALLA/oai:DiVA.org:su-863
Date January 2006
CreatorsBlomberg, Mattias
PublisherStockholm University, Department of Physics, Stockholm : Fysikum
Source SetsDiVA Archive at Upsalla University
LanguageEnglish
Detected LanguageEnglish
TypeDoctoral thesis, comprehensive summary, text

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