<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>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:su-863 |
| Date | January 2006 |
| Creators | Blomberg, Mattias |
| Publisher | Stockholm University, Department of Physics, Stockholm : Fysikum |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
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