Sandbox Reserved 760: Difference between revisions
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The complex dissociatesto form Feox(MgADP)2 + MoFered, which is believed to be the rate-limiting step for the whole substrate conversion. The rate of the complex dissociation is about 5s-1 under saturating conditions. The electron collected by MoFe-protein is used for substrate reduction and the Fe protein goes back to its starting point to end the redox or the Fe-protein cycle. | The complex dissociatesto form Feox(MgADP)2 + MoFered, which is believed to be the rate-limiting step for the whole substrate conversion. The rate of the complex dissociation is about 5s-1 under saturating conditions. The electron collected by MoFe-protein is used for substrate reduction and the Fe protein goes back to its starting point to end the redox or the Fe-protein cycle. | ||
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The substrate reduction cycle''': The substrate reduction cycle is not well known either but it is supposed that the Fe-protein cycle limits the electron transport to the active site of nitrogenase since it donates the electrons used in the substrate reduction. [[Image: | The substrate reduction cycle''': The substrate reduction cycle is not well known either but it is supposed that the Fe-protein cycle limits the electron transport to the active site of nitrogenase since it donates the electrons used in the substrate reduction. [[Image:tapa1.jpg|frame|right]] | ||
Thorneley & Lowe proposed a scheme for nitrogen fixation. Starting from the resting state E0 which represents the MoFe-protein at an oxidized state, one electron and proton are added to the protein which leads to the E1H1state as depicted in diagram. The notation ExHy describes the protein with x electrons and y protons added to the resting state. After the next electron-proton transfer step, reaching E2H2, there is a chance that the H2 production which would lead back to the resting state. This highly depends on the electron flux, that is, the concentration of the Fe-protein and its supply of the electrons needed compared to the concentration of the MoFe-protein. When there is a low flux, there is a low concentration of the Fe-protein compared to the MoFe-protein, the E1H1 state builds up H2 whereas the E2H2 is removed by evolving H2. | Thorneley & Lowe proposed a scheme for nitrogen fixation. Starting from the resting state E0 which represents the MoFe-protein at an oxidized state, one electron and proton are added to the protein which leads to the E1H1state as depicted in diagram. The notation ExHy describes the protein with x electrons and y protons added to the resting state. After the next electron-proton transfer step, reaching E2H2, there is a chance that the H2 production which would lead back to the resting state. This highly depends on the electron flux, that is, the concentration of the Fe-protein and its supply of the electrons needed compared to the concentration of the MoFe-protein. When there is a low flux, there is a low concentration of the Fe-protein compared to the MoFe-protein, the E1H1 state builds up H2 whereas the E2H2 is removed by evolving H2. | ||
If flux of the Fe-protein is high, E2H2 will again be reduced and protonated, leading to E3H3, which again can produce H2. Dinitrogen then binds only when there are up to 3 or 4 electrons supplied.The binding of dinitrogen produces one H2 and leads to E3HN2. In its turn, H2 can act as an inhibitor to N2. The state E3H3 may be reduced to E4H4 which then can bind N2 along with H2 production. The protein goes back to its oxidized state if no more substrate is available to be reduced and N2 is protonated until NH3 is released. | If flux of the Fe-protein is high, E2H2 will again be reduced and protonated, leading to E3H3, which again can produce H2. Dinitrogen then binds only when there are up to 3 or 4 electrons supplied.The binding of dinitrogen produces one H2 and leads to E3HN2. In its turn, H2 can act as an inhibitor to N2. The state E3H3 may be reduced to E4H4 which then can bind N2 along with H2 production. The protein goes back to its oxidized state if no more substrate is available to be reduced and N2 is protonated until NH3 is released. | ||
