PubMed · 7702273
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
P Mathelier-Fusade, F Leynadier. 1994. [Cold urticaria].. https://pubmed.ncbi.nlm.nih.gov/7702273/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The photochemically trapped bacteriopheophytin (BPh) b radical anion in the active branch (phi(*-)A) of reaction centers (RCs) from Blastochloris (formerly called Rhodopseudomonas) viridis is characterized by 1H-ENDOR as well as optical absorption spectroscopy. The two site-directed mutants YF(M208) and YL(M208), in which tyrosine at position M208 is replaced by phenylalanine and leucine, respectively, are investigated and compared with the wild type. The residue at M208 is in close proximity to the primary electron donor, P, the monomeric bacteriochlorophyll (BCh1), B(A), and the BPh, phiA, that are involved in the transmembrane electron transfer to the quinone, Q(A), in the RC. The analysis of the ENDOR spectra of (phi(*-)A at 160 K indicates that two distinct states of phi(*-)A are present in the wild type and the mutant YF(M208). Based on a comparison with phi(*-)A in RCs of Rhodobacter sphaeroides the two states are interpreted as torsional isomers of the 3-acetyl group of phiA. Only one phi(*-)A state occurs in the mutant YL(M208). This effect of the leucine residue at position M208 is explained by steric hindrance that locks the acetyl group in one specific position. On the basis of these results, an interpretation of the optical absorption difference spectrum of the state phi(*-)AQ(*-)A is attempted. This state can be accumulated at 100 K and undergoes an irreversible change between 100 and 200 K [Tiede et al., Biochim. Biophys. Acta 892 (1987) 294-302]. The corresponding absorbance changes in the BCh1 Q(x) and Q(y) regions observed in the wild type also occur in the YF(M208) mutant but not in YL(M208). The observed changes in the wild type and YF(M208) are assigned to RCs in which the 3-acetyl group of phiA changes its orientation. It is concluded that this distinct structural relaxation of phiA can significantly affect the optical properties of B(A) and contribute to the light-induced absorption difference spectra.
Unlike any volcanic behavior ever observed on Earth, the plume from Prometheus on Io has wandered 75 to 95 kilometers west over the last 20 years since it was first discovered by Voyager and more recently observed by Galileo. Despite the source motion, the geometric and optical properties of the plume have remained constant. We propose that this can be explained by vaporization of a sulfur dioxide and/or sulfur "snowfield" over which a lava flow is moving. Eruption of a boundary-layer slurry through a rootless conduit with sonic conditions at the intake of the melted snow can account for the constancy of plume properties.
Sinorhizobium meliloti growth is affected when the incubation temperature is lower than 22 degrees C. In culture media containing glucose or fructose (1%, w/v), the doubling time at 19 degrees C was about 6.25 h during the exponential growth phase, while it was 2.75 h at 30 degrees C; at 17 degrees C it was three-fold higher than at 30 degrees C. Modifications in the bacterial metabolism explain the doubling time increase when bacteria are incubated at low temperature. We determine here, the phosphoenolpyruvate carboxykinase (PEPCK) activity increases when S. meliloti cells first grown at 30 degrees C are shifted at 17 degrees C and incubated for 10 h at this low temperature; we noted the PEPCK activity was three-fold higher in cells incubated in media containing glucose and shifted from 30 to 17 degrees C than in cells maintained at 30 degrees C, while it was only 1.5-fold higher in cells grown in media containing fructose.