Measurements of residual dipolar couplings in peptide inhibitors weakly aligned by transient binding to peptide amyloid fibrils**

In this communication, we suggest that transferred residual dipolar couplings (trRDCs) can be employed to restrain the structure of peptide inhibitors transiently binding to beta-amyloid fibrils. The effect is based on the spontaneous alignment of amyloid fibrils with the fibril axis parallel to the magnetic field. This alignment is transferred to the transiently binding peptide inhibitor and is reflected in the size of the trRDCs. We find that the peptide inhibitor adopts a beta-sheet conformation with the backbone N-H and C-H dipolar vectors aligned preferentially parallel and perpendicular, respectively, to the fibril axis.     

Two distinct cis-acting elements are involved in light-dependent activation of the pea elip promoter

Light activation of the pea (Pisum sativum) elip gene promoter was analysed in transgenic plants and in transiently transfected plant protoplasts. A series of promoter deletions fused to the gusA reporter was tested, and the results obtained by the two experimental approaches were in good agreement. We identified two nucleotide sequence elements involved in light-regulated expression of the elip gene. One element is similar to the GT1 binding site of the rbcS-3A gene, and the other resembles a G-box-like ACGT element. The region containing both elements was able to confer light responsiveness on a heterologous basic promoter. Electrophoretic mobility shift assays demonstrated that each element is specifically recognized by DNA-binding proteins present in nuclear extracts from pea seedlings. The G-box-like ACGT element is necessary but not sufficient for light inducibility, indicating that the two elements act together in confering light responsiveness.     

Biozid-Belastungen bei weiblichen Kohlmeisen(Parus major) w?hrend der Brutzeit

Summary For investigations about changes of the genital system during breeding 7 female Great Tits were killed. Their carcasses were additionally examined for pesticide residues. The values of pesticides lay at the limit of indication, so that any damage for the population of Great Tits in the Siebengebirge (near Bonn) can be excluded.     

Modeling the hypothalamus–pituitary–adrenal system: homeostasis by interacting positive and negative feedback

The hypothalamus–pituitary–adrenal (HPA) system is closely related to stress and the restoration of homeostasis. This system is stimulated in the second half of the night, decreases its activity in the daytime, and reaches the homeostatic level during the late evening. In this paper, we derive and discuss a novel model for the HPA system. It is based on three simple rules that constitute a principle of homeostasis and include only the most substantive physiological elements. In contrast to other models, its main components include, apart from the conventional negative feedback ingredient, a positive feedback loop. To validate the model, we present a parameter estimation procedure that enables one to adapt the model to clinical observations. Using this methodology, we are able to show that the novel model is capable of simulating clinical trials. Furthermore, the stationary state of the system is investigated. We show that, under mild conditions, the system always has a well-defined set-point, which reflects the clinical situation to be modeled. Finally, the computed parameters may be interpreted from a physiological point of view, thereby leading to insights about diseases like depression, obesity, or diabetes.     

Identification of a new class of nitrogen fixation genes in Rhodobacter capsalatus: a putative membrane complex involved in electron transport to nitrogenase

DNA sequence analysis of a 12236 by fragment, which is located upstream of nifE in Rhodobacter capsulatus nif region A, revealed the presence of ten open reading frames. With the exception of fdxC and fdxN, which encode a plant-type and a bacterial-type ferredoxin, the deduced products of these coding regions exhibited no significant homology to known proteins. Analysis of defined insertion and deletion mutants demonstrated that six of these genes were required for nitrogen fixation. Therefore, we propose to call these genes rnfA, rnfB, rnfC, rnfD, rnfE and rnfF (for Rhodobacter nitrogen fixation). Secondary structure predictions suggested that the rnf genes encode four potential membrane proteins and two putative iron-sulphur proteins, which contain cysteine motifs (C-X₂-C-X₂-C-X₃-C-P) typical for [4Fe-4S] proteins. Comparison of the in vivo and in vitro nitrogenase activities of fdxN and rnf mutants suggested that the products encoded by these genes are involved in electron transport to nitrogenase. In addition, these mutants were shown to contain significantly reduced amounts of nitrogenase. The hypothesis that this new class of nitrogen fixation genes encodes components of an electron transfer system to nitrogenase was corroborated by analysing the effect of metronidazole. Both the fdxN and rnf mutants had higher growth yields in the presence of metronidazole than the wild type, suggesting that these mutants contained lower amounts of reduced ferredoxins.     

The stereochemical course of the reaction mechanism of trehalose phosphorylase from Schizophyllum commune

Phosphorolysis of α,α-trehalose catalyzed by trehalose phosphorylase from the basidiomycete Schizophyllum commune proceeds via net retention of anomeric configuration and yields α- -glucose 1-phosphate and α- -glucose as the products. In reverse reaction, only the α-anomers of -glucose 1-phosphate and -glucose are utilized as glucosyl donor and acceptor, respectively, and give exclusively the α,α-product. Trehalose phosphorylase converts α- -glucose 1-fluoride and phosphate into α- -glucose 1-phosphate, a reaction requiring the stereospecific protonation of the glucosyl fluoride by a Brønsted acid. The results are discussed with regard to a plausible reaction mechanism of fungal trehalose phosphorylase.     

Genotype-specific differences in chilling tolerance of maize in relation to chilling-induced changes in water status and abscisic acid accumulation

Four inbred maize lines differing in chilling tolerance were used to study changes in water status and abscisic acid (ABA) levels before, during and after a chilling period. Seedlings were raised in fertilized soil at 24/22°C (day/night), 70% relative humidity. and a 12-h photoperiod with 200 μmol m⁻² s⁻¹ from fluorescent tubes. At an age of 2 weeks the plants were conditioned at 14/12°C for 4 days and then chilled for 5 days at 5/3°C. The other conditions (relative humidity, quantum flux, photoperiod) were unchanged. After the chilling period the plants were transferred to the original conditions for recovery. The third leaves were used to study changes in leaf necrosis, ion efflux, transpiration, water status and ABA accumulation. Pronounced differences in chilling tolerance between the 4 lines as estimated by necrotic leaf areas, ion efflux and whole plant survival were observed. Conditioning significantly increased tolerance against chilling at 5/3°C in all genotypes. The genotypes with low chilling tolerance had lower water and osmotic potentials than the more tolerant genotypes during a chilling period at 5/3°C. These differences were related to higher transpiration rates and lower diffusive resistance values of the more susceptible lines. During chilling stress at 5/3°C ABA levels were quadrupled. Only a small rise was measurable during conditioning at 14/12°C. However, conditioning enhanced the rise of ABA during subsequent chilling. ABA accumulation in the two lines with a higher chilling tolerance was triggered at a higher leaf water potential and reached higher levels than in the less tolerant lines. We conclude that chilling tolerance in maize is related to the ability for fast and pronounced formation of ABA as a protective agent against chilling injury.     

The protein inhibitor of neuronal nitric oxide synthase (PIN): characterization of its action on pure nitric oxide synthases

Neuronal NO synthase (nNOS) was discovered recently to interact specifically with the protein PIN (protein inhibitor of nNOS) [Jaffrey, S.R. and Snyder, S.H. (1996) Science 274, 774–777]. We have studied the effects on pure NOS enzymes of the same GST-tagged PIN used in the original paper. Unexpectedly, all NOS isoenzymes were inhibited. The IC₅₀ for nNOS was 18±6 μM GST-PIN with 63 nM nNOS after 30 min at 37°C. Uncoupled NADPH oxidation was inhibited similarly, whereas cytochrome c reductase activity, the K_M for l-arginine, and dimerization were unaffected. We reconsider the physiological role of PIN in the light of these results.