Dehydroascorbate reductase (DHAR) is a key component of the ascorbate recycling system. Three functional DHAR genes are encoded in the Arabidopsis genome. Ozone exposure increased the expression of the cytosolic DHAR (cytDHAR) gene alone. We characterized an Arabidopsis mutant with a deficient cytDHAR. The mutant completely lacked cytDHAR activity and was highly ozone sensitive. The amounts of total ascorbate and glutathione were similar in both lines, but the amount of apoplastic ascorbate in the mutant was 61.5% lower. These results indicate that the apoplastic ascorbate, which is generated through the reduction of DHA by cytDHAR, is important for ozone tolerance.
cDNA clones which strongly hybridized with a 3.1 kb mRNA from mouse macrophages and macrophage cell lines and weakly with mRNA from P815 but not from a variety of other cell lines and tissues were isolated from cDNA libraries constructed using mRNA from murine macrophage cell lines and peritoneal macrophages. Treatment of a macrophage cell line with macrophage stimulators significantly enhanced transcription of the mRNA. Sequencing analysis of these clones demonstrated that the cDNA consisted of 3036 bp insert containing a 2478 bp open reading frame followed by a 538 bp 3' untranslated region. The amino acid sequence, deduced from the nucleotide sequence of the cDNA, predicted a protein containing a signal peptide, an extracellular region, a transmembrane domain, and a cytoplasmic tail. The extracellular region had five putative N-glycosylation sites and a cysteine-rich domain, whereas the cytoplasmic region consisted of a proline-rich amino acid sequence significantly similar to CD2. SDS-PAGE and NEPHGE SDS-PAGE analysis of the immunoprecipitated membrane of the macrophage cell lines prepared by using rabbit anti-MS2 peptide antibody raised against a synthetic peptide preparation relative to a hydrophilic region of the MS2 amino acid sequence confirmed that MS2 protein is a cross-linked protein having approximate molecular sizes of 89 kd and pl 6.5-7.0. These results show that MS2 protein is a novel cell surface antigen expressed mainly in monocytic lineages.
The Ag-Sn alloys prepared by mechanical alloying technique have been studied as negative electrode materials for lithium-ion batteries. With optimized compositions and structure morphologies, both Ag 52 Sn 48 and Ag 46 Sn 54 composite electrodes exhibit an initial capacity of ϳ800 mAh/g and maintain a reversible capacity of above 350 mAh/g for more than 50 cycles. Even after 300 cycles, the former still keeps a reversible capacity of approximately 200 mAh/g. Typically, the structural changes of Ag 52 Sn 48 electrode accompanied by Li insertion/extraction processes were examined by means of X-ray diffraction analyses. The results reveal that the composite alloy consisting of -Sn and Ag 3 Sn phases transforms mostly into that of ternary lithiated phase during Li insertion and recovers to one involving -Sn, Ag 3 Sn, and residual Ag 2 LiSn phases after Li extraction. It is considered that the composite structure containing the ternary lithiated phase, which is formed during the first cycle, is beneficial for the improvement of the cycle life of the Ag-Sn alloy electrode, although the residual lithiated product possibly leads to an increase of the irreversible loss.
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