Contributions of algae to GPP and DOC production in an Alaskan fen: effects of historical water table manipulations on ecosystem responses to a natural flood

The role of algae in the metabolism of northern peatlands is largely unknown, as is how algae will respond to the rapid climate change being experienced in this region. In this study, we examined patterns in algal productivity, nutrients, and dissolved organic carbon (DOC) during an uncharacteristically wet summer in an Alaskan rich fen. Our sampling was conducted in three large-scale experimental plots where water table position had been manipulated (including both drying and wetting plots and a control) for the previous 4 years. This study allowed us to explore how much ecosystem memory of the antecedent water table manipulations governed algal responses to natural flooding. Despite no differences in water table position between the manipulated plots at the time of sampling, algal primary productivity was consistently higher in the lowered water table plot compared to the control or raised water table plots. In all plots, algal productivity peaked immediately following seasonal maxima in nutrient concentrations. We found a positive relationship between algal productivity and water-column DOC concentrations (r (2) = 0.85, P < 0.001). Using these data, we estimate that algae released approximately 19% of fixed carbon into the water column. Algal exudates were extremely labile in biodegradability assays, decreasing by more than 55% within the first 24 h of incubation. We suggest that algae can be an important component of the photosynthetic community in boreal peatlands and may become increasingly important for energy flow in a more variable climate with more intense droughts and flooding.     

On‐resin synthesis of novel arginine‐isostere peptides bearing substituted amidine headgroups

A methodology is presented for the facile synthesis of Arg‐containing peptides modified at the guanidine headgroup as substituted amidine cores. This process allows for the iterative construction of these Arg isosteres while the peptide is being built out on the solid support, providing a high potential for diversity in substitution pattern in the resulting peptide. A series of N‐Pmc‐substituted thioamides were condensed with deprotected δ‐N Orn‐bearing peptides while attached to the solid support using Mukaiyama's reagent as coupling reagent, yielding isosteric Arg‐containing analogs. Peptides were cleaved using trimethylsilyl trifluoromethanesulfonate/TFA and analyzed in their crude form in order to illustrate the amenability of this process toward production of peptide isolates in high crude purity. Arg‐containing peptides having a single Arg isostere were utilized to show the general utility of this approach as well as a multiple‐Arg‐containing construct, illustrating the amenability of this method toward stepwise construction of differently substituted amidine headgroups within the same peptide. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Loss of tafazzin results in decreased myoblast differentiation in C2C12 cells: A myoblast model of Barth syndrome and cardiolipin deficiency

Barth syndrome (BTHS) is an X-linked genetic disorder resulting from mutations in the tafazzin gene (TAZ), which encodes the transacylase that remodels the mitochondrial phospholipid cardiolipin (CL). While most BTHS patients exhibit pronounced skeletal myopathy, the mechanisms linking defective CL remodeling and skeletal myopathy have not been determined. In this study, we constructed a CRISPR-generated stable tafazzin knockout (TAZ-KO) C2C12 myoblast cell line. TAZ-KO cells exhibit mitochondrial deficits consistent with other models of BTHS, including accumulation of monolyso-CL (MLCL), decreased mitochondrial respiration, and increased mitochondrial ROS production. Additionally, tafazzin deficiency was associated with impairment of myocyte differentiation. Future studies should determine whether alterations in myogenic determination contribute to the skeletal myopathy observed in BTHS patients. The BTHS myoblast model will enable studies to elucidate mechanisms by which defective CL remodeling interferes with normal myocyte differentiation and skeletal muscle ontogenesis.     

Bronchial hyperreactivity in patients who cough after receiving angiotensin converting enzyme inhibitors

Angiotensin converting enzyme inhibitors cause cough in some patients, but the mechanism of this effect is not known. Six patients in whom these inhibitors had caused cough and a further two patients in whom they were suspected to have caused worsening of bronchial asthma were studied. Nine patients in whom angiotensin converting enzyme inhibitors had not been associated with cough served as controls. In the controls lung function and bronchial reactivity were measured once; for the study patients these and the cough index were measured twice before rechallenge for two weeks with an angiotensin enzyme inhibitor and once afterwards. Rechallenge with drug for two weeks caused a significant decrease in the mean concentration of histamine causing a 35% fall in airways conductance and a significant increase in the cough index. Patients with cough showed bronchial hyperactivity compared with the controls, which increased after rechallenge with the inhibitors.Cough associated with converting enzyme inhibitors may be a variant of the cough in asthma.