Nitrogenase is the only enzyme that can convert atmospheric dinitrogen (N2) into the biologically usable ammonia. To achieve this multi-electron redox process, the nitrogenase component proteins, MoFe-protein (MoFeP) and Fe-protein (FeP), repeatedly associate and dissociate in an ATP dependent manner, where one electron is transferred from FeP to MoFeP per association. Here, we provide evidence for the first time that encounter complexes between FeP and MoFeP play a functional role in nitrogenase turnover. The encounter complexes are stabilized by electrostatic interactions involving a positively charged patch on the β-subunit of MoFeP. Three single mutations (βAsn399Glu, βLys400Glu, and βArg401Glu) in this patch were generated in Azotobacter vinelandii MoFeP. All of the resulting variants displayed decreases in specific catalytic activity, with the βK400E mutation showing the largest effect. As simulated by the Thorneley-Lowe kinetic scheme, this single mutation lowered the rate constant for FeP-MoFeP association five-fold. We also found that the βK400E mutation did not affect the coupling of ATP hydrolysis with electron transfer (ET) between FeP and MoFeP. These data suggest a mechanism where FeP initially forms encounter complexes on the MoFeP β-subunit surface en route to the ATP-activated, ET-competent complex over the αβ-interface.
New inorganic-organic hybrids were synthesized through the reaction of castor oil (CO) or epoxidized castor oil (ECO) with tetraethoxysilane (TEOS). The mass proportions of ECO/TEOS varied from 90:10 to 60:40, and films of the material were thermally cured. An IR spectroscopy analysis was performed, and macro-and microscopic properties such as adhesion, hardness, swelling in toluene, microstructure (scanning electron microscopy), and T g were investigated as a function of the proportion of their inorganic-organic precursor. Morphologic studies showed that the hybrid films were homogeneous when lower proportions of the inorganic precursors were used. Hardness and tensile strength increased with TEOS concentration, whereas swelling in toluene decreased with TEOS concentration. Good adhesion was observed throughout the hybrid series. Paper no. J11172 in JAOCS 83, 147-151 (February 2006). FIG. 1. Castor oil and epoxidized castor oil structures. JAOCS, Vol. 83, no. 2 (2006) FIG. 8. IR spectra of cured films of ECO and ECO70/TEOS30. For abbreviations see Figure 3. Wavelength (cm − −1 )
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