ABSTRACT
Copper (Cu) isotopes can be a useful tool to constrain the interaction of water and the environment, but they have not been widely applied to riverine research in the preceding decades. Isotopically heavy Cu in rivers (global average: about +0.7) compared to rocks (at about 0) has been attributed to: a) the mobilization of heavy Cu during oxidative weathering, and b) partitioning between an isotopically heavy, organically complexed dissolved pool, and an isotopically light pool adsorbed to particulates. Here, we report Cu concentrations and isotope ratios of the main stream of the Yangtze River and its several tributaries. We find that the Yangtze River exhibits anomalously heavy Cu isotope compositions compared to other rivers: δ65CuNIST 976 of dissolved Cu for the main stream, from Chongqing to Nanjing, ranges from +0.59 to +1.65, while the tributaries vary from +0.48 to +1.20. A negative correlation is observed between Cu concentrations and Cu isotope compositions. We attribute the anomalous Cu isotope geochemistry of the Yangtze River to two key features of the basin: first, the influence of the Three Gorges Dam (TGD), and second, the presence of extensive Cu sulphide deposits close to the lower reaches of the river. In the upper reaches, downstream towards the TGD, δ65Cu values increase as Cu concentrations decrease, reflecting the preferential adsorption of light Cu by sedimenting particulate phases. δ65Cu values continue to increase to a maximum of +1.65 in the middle reaches, at Guangxingzhou. The lower reaches, from Jiujiang to Tongling, are characterized by less positive values of δ65Cu (at about +0.60), due to the oxidative weathering of Cu sulphide deposits. The overall Cu-δ65Cu trend in the river reflects mixing of these waters from the lower reaches, influenced by Cu sulphides, with waters from upstream, which have lower Cu concentrations and elevated δ65Cu values.
ABSTRACT
Nuclear factor-erythroid number 2 (NF-E2) is a positive regulatory, DNA binding transcription factor for gene expression in erythroid and megakaryocytic cells. To further understand the mechanisms of NF-E2 function, we used expression cloning to identify coregulators interacting with the erythroid-specific subunit of NF-E2, p45. We have isolated a protein, NAPP2, which contains an aspartic-acid- and glutamic-acid-rich region and a nuclear localization signal. The gene encoding NAPP2, PEX14, is located on chromosome 1p36 and is ubiquitously expressed. The domains of interaction in vitro and in vivo between p45 and NAPP2 were mapped by a yeast two-hybrid system and cotransfection experiments. In mammalian cell culture, ectopically expressed NAPP2 inhibited p45-directed transcriptional activation. Furthermore, NAPP2 functions as a corepressor and interacts specifically with histone deacetylase l (HDAC1), but not HDAC2 or HDAC3. NAPP2 is thus potentially a negative coregulator of NF-E2. NAPP2 is identical to PEX14, an integral membrane protein essential for protein docking onto the peroxisomes. These studies have identified a novel, bifunctional protein capable of acting as a transcriptional corepressor and a polypeptide transport modulator. They also suggest that NF-E2 may function both positively and negatively in the transcription regulation of specific erythroid and megakaryocytic genes.