Gating mechanisms conformational changes

NADPH oxidation and NO synthesis by the enzyme, it supports a role for reduction of the heme iron in catalysis, and may explain why NOS functions only as an NADPH-dependent reductase in the absence of bound calmodulin (Klatt et ai, 1993). The mechanism of calmodulin gating is envisioned to involve a conformational change between the reductase and oxygenase domains of NOS, such that an electron transfer between the terminal flavin and heme iron becomes possible. Calmodulin may also have a distinct role within the NOS reductase domain, in that its binding dramatically increases reductase activity of the enzyme toward cytochrome c (Klatt et al., 1993 Heinzel et al., 1992). However, it is clear that several other NOS functions occur independent of calmodulin, including the binding of L-arginine and NADPH, and transfer of NADPH-derived electrons into the flavins (Abu-Soud and Stuehr, 1993). 

The mechanism of proton translocation in complexes I and IV is not yet understood. Here, the electron-transfer reactions may cause protein conformational changes that open gates for proton movement first on one side of the membrane and then on the other. 

Qin L et al (2009) Redox dependent conformational changes in cytochrome c oxidase suggest a gating mechanism for proton uptake. Biochem 48 5121-5130 PDBID 3FYI... 

Comprehensive laser flash photolysis stndies on chicken and human SO have probed the rates of intermolecular electron transfer (lET, see Intermolecular) between the Mo and heme centers. Data are consistent with a CEPT mechanism interconverting Fe V[Mo02] " and Fe /[MoO(OH)]+ centers. To account for the wide range of lET rates (20-1400 s ), it has been proposed that protein conformational changes effectively gate lET by changing the Fe- Mo distance. 

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