Methanococcus voltae carries genetic information for four [NiFe] hydrogenases. Two of the hydrogenases are predicted to contain selenocysteine on the basis of in-frame TGA codons, while the genes encoding the two other enzymes contain cysteine codons at homologous positions. Their predicted subunit compositions and their electron acceptor specificities are similar to those of the respective selenium-containing enzymes. The selenium-containing hydrogenases have been purified and characterized. Only one of them reduces the deazaflavin F(420). The activity of the F(420)-nonreducing enzyme is exceptionally high. The selenium atom has been shown by EPR spectroscopy to be a ligand to the Ni atom in the primary reaction centers in both enzymes. The spectroscopic analyses also yielded a description of the electronic configuration around the NiFe center at different oxidation states and in the presence of the competitive inhibitor, CO. The genes encoding the selenium-free hydrogenases are expressed only in the absence of selenium. They are linked by an intergenic region in which regulatory cis elements were defined by employing reporter gene constructs and site-directed mutagenesis.
The properties of the heme, flavin mononucleotide (FMN) and FeS domains of P450 RhF, from Rhodococcus sp. NCIMB 9784, expressed separately and in combination are analysed. The nucleotide preference, imidazole binding and reduction potentials of the heme and FMN domains are unaltered by their separation. The intact enzyme is monomeric and the flavin is confirmed to be FMN. The two one-electron reduction potentials of the FMN are À240 and À270 mV. The spectroscopic and thermodynamic properties of the FeS domain, masked in the intact enzyme, are revealed for the first time, confirming it as a 2Fe-2S ferredoxin with a reduction potential of À214 mV.
Ion-sensitive field-effect transistors based on silicon nanowires are promising candidates for the detection of chemical and biochemical species. These devices have been established as pH sensors thanks to the large number of surface hydroxyl groups at the gate dielectrics which makes them intrinsically sensitive to protons. To specifically detect species other than protons, the sensor surface needs to be modified. However, the remaining hydroxyl groups after functionalization may still limit the sensor response to the targeted species.Here, we describe the influence of competing reactions on the measured response using monolayer of calcium-sensitive molecules. We identify the residual pH response as the key parameter limiting the sensor response. The competing effect of pH or any other relevant reaction at the sensor surface has therefore to be included to quantitatively understand the sensor response and prevent misleading interpretations.
A transistor-type heater is presented, which has been developed to regulate the temperature of microhotplates in industrial CMOS technology. The heating transistor preserves its transistor characteristics up to 350 C and shows almost linear heating characteristics at temperatures higher than 100 C. The temperature can be controlled by adjusting the transistor source/gate voltage. Sensor measurements for CO are presented in two different sensing modes: chemoresistive readout and calorimetric readout by means of monitoring changes in the source/gate voltage which is required to keep the microhotplate temperature at the preset value. The device is part of an approach to monolithically integrate metal-oxide chemical sensors with circuitry.Index Terms-Metal-oxide gas sensor, microhotplate, MOSFET heater.
Ionic gradients play a crucial role in the physiology of the human body, ranging from metabolism in cells to muscle contractions or brain activities. To monitor these ions, inexpensive, label-free chemical sensing devices are needed. Field-effect transistors (FETs) based on silicon (Si) nanowires or nanoribbons (NRs) have a great potential as future biochemical sensors as they allow for the integration in microscopic devices at low production costs. Integrating NRs in dense arrays on a single chip expands the field of applications to implantable electrodes or multifunctional chemical sensing platforms. Ideally, such a platform is capable of detecting numerous species in a complex analyte. Here, we demonstrate the basis for simultaneous sodium and fluoride ion detection with a single sensor chip consisting of arrays of gold-coated SiNR FETs. A microfluidic system with individual channels allows modifying the NR surfaces with self-assembled monolayers of two types of ion receptors sensitive to sodium and fluoride ions. The functionalization procedure results in a differential setup having active fluoride- and sodium-sensitive NRs together with bare gold control NRs on the same chip. Comparing functionalized NRs with control NRs allows the compensation of non-specific contributions from changes in the background electrolyte concentration and reveals the response to the targeted species.
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