The class III anaerobic ribonucleotide reductases (RNRs) studied to date couple the reduction of ribonucleotides to deoxynucleotides with the oxidation of formate to CO 2 . Here we report the cloning and heterologous expression of the Neisseria bacilliformis class III RNR and show that it can catalyze nucleotide reduction using the ubiquitous thioredoxin/thioredoxin reductase/NADPH system. We present a structural model based on a crystal structure of the homologous Thermotoga maritima class III RNR, showing its architecture and the position of conserved residues in the active site. Phylogenetic studies suggest that this form of class III RNR is present in bacteria and archaea that carry out diverse types of anaerobic metabolism.T he class III ribonucleotide reductases (RNRs) are glycyl radical enzymes present in many strict and facultative anaerobes that catalyze the conversion of nucleotides to deoxynucleotides (1, 2) via a mechanism involving complex free radical chemistry and are largely responsible for providing the balanced pool of deoxynucleotides required for DNA synthesis and repair (3). The class III RNRs that have been characterized thus far obtain the reducing equivalents required to make deoxynucleoside triphosphates (dNTPs) from the oxidation of formate to CO 2 (4). Here we report a second subtype of class III RNR from Neisseria bacilliformis, which can obtain its reducing equivalents from the thioredoxin (TrxA)/thioredoxin reductase (TrxB)/ NADPH system. RNRs provide the only pathway for de novo biosynthesis of dNTPs (5). They share a structurally homologous active site architecture in the α subunit and a partially conserved, radicalbased reduction mechanism. RNRs have been isolated and characterized from all kingdoms of life and, based on the characterization of these proteins thus far, are divided into three classes (I, II, and III) according to the metallo-cofactor used to generate a thiyl radical that initiates the radical-dependent reduction chemistry (6). The class I RNRs use cofactors generated by the reaction of reduced metals (Fe, Mn, and Fe/Mn) and O 2 and are present only in aerobic organisms. The class II RNRs use adenosylcobalamin in an O 2 -independent reaction and are present in both aerobes and anaerobes. The class III RNR uses an O 2 -sensitive glycyl radical (G•) (2) situated in the α protein (NrdD), which is generated by a separate activating enzyme (NrdG) via radical S-adenosylmethionine (SAM)-[4Fe4S] 1+ chemistry (7,8). The class III RNRs are only found in facultative and obligate anaerobes. A second distinction between the three classes has been the source of the reducing equivalents for nucleotide reduction. In the class I and II RNRs, they are provided by a redoxin (thioredoxin, glutaredoxin, or NrdH), which is rereduced by thioredoxin reductase and NADPH (9-11). In contrast, for the bacteriophage T4 (12), its Gram-negative host Escherichia coli (1), and the Gram-positive Lactococcus lactis (13), the only class III RNRs characterized in detail to date, nucleotide reduction i...

A kinetic study for isothermal melt crystallization of CaO-SiO 2-CaF 2-based mold fluxes with different basicity of 0.94 and 1.34 has been carried out systematically by DSC measurements. The kinetic parameters were determined by Johnson-Mehl-Avrami equation. The average Avrami exponent of cuspidine (3CaOAE2SiO 2 AECaF 2) crystallization for mold flux of lower basicity (0.94) is calculated to be 3.1, implying that the crystallization mode is instantaneous nucleation followed by 3-dimensional growth. For the mold flux of higher basicity (1.34), the average Avrami exponent of cuspidine equals to 3.4, strongly suggesting that the growth is still 3 dimensional but the nucleation should be continuous. It was found that the effective crystallization rate constant for both mold fluxes increases as the crystallization temperature decreases, showing that the crystallization rate could be governed by nucleation rate. The negative effective activation energy indicates an anti-Arrhenius behavior for crystallization of the mold fluxes studied. Therefore, it is concluded that the melt crystallization for the commercial mold fluxes will be determined by thermodynamics of nucleation which is relevant to degree of undercooling. The morphology of cuspidine crystals observed by SEM agreeds well with the isothermal crystallization kinetics results.

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In this study, a low-altitude remote sensing (LARS) observation system was employed to observe a rapidly changing coastal environment-owed to the regular opening of the sluice gate of the Saemangeum seawall-off the west coast of South Korea. The LARS system uses an unmanned aerial vehicle (UAV), a multispectral camera, a global navigation satellite system (GNSS), and an inertial measurement unit (IMU) module to acquire geometry information. The UAV system can observe the coastal sea surface in two dimensions with high temporal (1 s−1) and spatial (20 cm) resolutions, which can compensate for the coarse spatial resolution of in-situ measurements and the low temporal resolution of satellite observations. Sky radiance, sea surface radiance, and irradiance were obtained using a multispectral camera attached to the LARS system, and the remote sensing reflectance (Rrs) was accordingly calculated. In addition, the hyperspectral radiometer and in-situ chlorophyll-a concentration (CHL) measurements were obtained from a research vessel to validate the Rrs observed using the multispectral camera. Multi-linear regression (MLR) was then applied to derive the relationship between Rrs of each wavelength observed using the multispectral sensor on the UAV and the in-situ CHL. As a result of applying MLR, the correlation and root mean square error (RMSE) between the remotely sensed and in-situ CHLs were 0.94 and ~0.8 μg L−1, respectively; these results show a higher correlation coefficient and lower RMSE than those of other, previous studies. The newly derived algorithm for the CHL estimation enables us to survey 2D CHL images at high temporal and spatial resolutions in extremely turbid coastal oceans.

Melt crystallization behavior of both the fluorine-containing and fluorine-free mold fluxes has been investigated using a single hot thermocouple technique (SHTT). By increasing the dew point of atmosphere from 223 K to 285.5 K (À50°C and 12.5°C), the primary crystalline phase of fluorine-containing mold flux was changed from cuspidine (Ca 4 Si 2 O 7 F 2 ) to Ca 2 SiO 4 with accelerated nucleation rates. Enhancement of fluorine evaporation due to hydroxyl is attributed to the main reason for the abnormal crystallization behavior of the fluorine-containing mold flux under humid atmosphere, which may bring a sticking-type breakout during the commercial continuous casting process. In contrast, the effect of water vapor on crystallization of fluorine-free mold flux was negligible. This implies that the application of fluorine-free mold fluxes can become a countermeasure to prevent the hydrogen-induced breakout during the continuous casting process under wet atmosphere.