In contrast to animal cells, plants use nitrate as a major source of nitrogen. Following the uptake of nitrate, this major macronutrient is fed into the vasculature for long-distance transport. The Arabidopsis thaliana shoot expresses the anion channel SLOW ANION CHANNEL1 (SLAC1) and its homolog SLAC1 HOMOLOGOUS3 (SLAH3), which prefer nitrate as substrate but cannot exclude chloride ions. By contrast, we identified SLAH2 as a nitrate-specific channel that is impermeable for chloride. To understand the molecular basis for nitrate selection in the SLAH2 channel, SLAC1 and SLAH2 were modeled to the structure of HiTehA, a distantly related bacterial member. Structure-guided site-directed mutations converted SLAC1 into a SLAH2-like nitrate-specific anion channel and vice versa. Our findings indicate that two pore-occluding phenylalanines constrict the pore. The selectivity filter of SLAC/SLAH anion channels is determined by the polarity of pore-lining residues located on alpha helix 3. Changing the polar character of a single amino acid side chain (Ser-228) to a nonpolar residue turned the nitrate-selective SLAH2 into a chloride/nitrate-permeable anion channel. Thus, the molecular basis of the anion specificity of SLAC/SLAH anion channels seems to be determined by the presence and constellation of polar side chains that act in concert with the two pore-occluding phenylalanines.

Pyruvate decarboxylase is a key enzyme in organisms whose energy metabolism is based on alcoholic fermentation. The enzyme catalyses the nonoxidative decarboxylation of 2-oxo acids in the presence of the cofactors thiamine diphosphate and magnesium ions. Pyruvate decarboxylase species from yeasts and plant seeds studied to date are allosterically activated by their substrate pyruvate. However, detailed kinetic studies on the enzyme from Neurospora crassa demonstrate for the first time the lack of substrate activation for a yeast pyruvate decarboxylase species. The quaternary structure of this enzyme species is also peculiar because it forms filamentous structures. The complex enzyme structure was analysed using a number of methods, including small-angle X-ray solution scattering, transmission electron microscopy, analytical ultracentrifugation and size-exclusion chromatography. These measurements were complemented by detailed kinetic studies in dependence on the pH. Structured digital abstractl PDC and PDC bind by light scattering (View Interaction: 1, 2) l PDC and PDC bind by cosedimentation in solution (View Interaction: 1, 2) l PDC and PDC bind by electron microscopy (View interaction) Abbreviations

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Summary: Acute myocardial infarction (AMI) leads to left ventricular dysfunction, the extent of which predicts mortality. We studied the effect of very early enalapril treatment in patients with lelt ventricular failure (Killip classification &HI) resulting from M I . In a double-blind randomized trial, patients on conventional treatment were started on placebo (PL, n = 15) or 2.5 mg enalapril (EN, n = 15) twice daily as early as 24 to 30 h after AM1 and were followed up over a period of 21 days. One patient died in each treatment group. There were three dropouts in the placebo group (progressive heart failure requiring antiotensn-converting enzyme inhibition) and one dropout in the enalapril group (malignant ventricular arrhythmias). Plasma atrial natriuretic peptide (ANP) and norepinephrine decreased siniilarty in both groups from elevated baseline concentrations. The patients with the highest baseline ANP levels died in both groups. EN: 579 fmoVml (mean 65.3 5 34.4 fmoVml), PL: 403 fmol/ml (mean 63.5 5 37.6 fmoVm1). Killip classification improved in 9 of I3 patients on enalapril but only in 5 of 11 patients on placebo. On echocardiography an increase in fractional shortening (FS) (3.2 +7.5%, p < 0.05) was found with enalapril only. Patients on placebo required more diuretics, and plasma aldosterone increased threefold. Thus, very early enalapril treatment may help prevent left ventricular failure after AMI. Extremely high initial plasma ANP concentrations may predict an unfavorable outcome.

Bundesgebiet meldeten sich dutzende ehemalige Samariterinnen und Samariter. Sie konnten teilweise von schon vollzogenen Neugründungen berichten oder ließen sich durch die Existenz eines Bundesvorstandes dazu motivieren, wieder aktiv zu werden. Aufgrund der vielen Rückmeldungen verschickte der Bundesvorstand am 1. August 1949 sein erstes Rundschreiben "an alle ehemaligen Arbeiter-Samariter der drei westlichen Besatzungszonen und den bereits bestehenden Kolonnen". Es war trotzdem notwendig, dass sich der Vorstand ab September 1949 einmal wöchentlich für drei Stunden traf, um die Korrespondenz zu erledigen.