The 'slow' pH-induced conformational transition of chloroplast fructose 1,6-bisphosphatase and the control of the Calvin cycle

A slow conformation change of chloroplastic reduced fructose bisphosphatase is detected upon raising the pH from 7 to 8 or upon lowering the pH from 8 to 7. These conformation changes are fully reversible. In the time scale investigated these processes occur in one step. Their time constants and their amplitudes have been determined and analyzed as a function of proton concentration. The results obtained are consistent with the view that upon ionization or protonation of a strategic ionizable group the protein undergoes a 'slow' conformational transition that may be followed by conventional fluorescence techniques. Since illumination brings about a pH rise of chloroplastic stroma from 7 to 8, the above results suggest that light activation of fructose bisphosphatase is at least in part due to a slow conformation change of this enzyme.     

pH modulation of transient state kinetics of enzymes. II. Transient state kinetics of plant cell wall acid phosphatase

The pre-steady-state kinetics of plant cell wall acid phosphatase has been investigated at different pH values. The approach of the steady stale lasts about 1 or 2 s and may be fitted with two exponential terms. For certain pH values the approach to the steady state exhibits damped oscillations. Plotting the sum and the product of the two time constants of these exponentials as a function of substrate concentration yields two straight lines. From the slopes and intercepts of these lines one may determine the values of rate and ionization constants involved in the reaction scheme. The results obtained are consistent with the view that the binding of the substrate to the enzyme does not induce a 'slow' conformation change of the enzyme. The enzyme reacts with its substrate while being mostly in its ionized form. Release of p-nitrophenol is also favoured by this ionized form of the enzyme. However, the hydrolysis of the phosphoryl-enzyme complex mostly occurs from the protonated form of the enzyme. The ionization constants of the free enzyme and of the various enzyme-ligand complexes are very similar.     

Reciprocal specialization in ecological networks

Theories suggest that food webs might consist of groups of species forming 'blocks', 'compartments' or 'guilds'. We consider ecological networks – subsets of complete food webs – involving species at adjacent trophic levels. Reciprocal specializations occur when (say) a pollinator (or group of pollinators) specializes on a particular flower species (or group of such species) and vice versa. Such specializations tend to group species into guilds. We characterize the level of reciprocal specialization for both antagonistic interactions – particularly parasitoids and their hosts – and mutualistic ones – such as insects and the flowers that they pollinate. We also examine whether trophic patterns might be 'palimpsests'– that is, there might be reciprocal specialization within taxonomically related species within a network, but these might be obscured when these relationships are combined. Reciprocal specializations are rare in all these systems when tested against the most conservative null model.     

Parents’ and Physicians’ Perceptions of Children’s Participation in Decision-making in Paediatric Oncology: A Quantitative Study

The goal is to present how shared decision-making in paediatric oncology occurs from the viewpoints of parents and physicians. Eight Swiss Pediatric Oncology Group centres participated in this prospective study. The sample comprised a parent and physician of the minor patient (<18 years). Surveys were statistically analysed by comparing physicians’ and parents’ perspectives and by evaluating factors associated with children’s actual involvement. Perspectives of ninety-one parents and twenty physicians were obtained for 151 children. Results indicate that for six aspects of information provision examined, parents’ and physicians’ perceptions differed. Moreover, parents felt that the children were more competent to understand diagnosis and prognosis, assessed the disease of the children as worse, and reported higher satisfaction with decision-making on the part of the children. A patient’s age and gender predicted involvement. Older children and girls were more likely to be involved. In the decision-making process, parents held a less active role than they actually wanted. Physicians should take measures to ensure that provided information is understood correctly. Furthermore, they should work towards creating awareness for systematic differences between parents and physicians with respect to the perception of the child, the disease, and shared decision-making.     

Cyclic AMP inhibits dedifferentiation in the cellular slime mold Dictyostelium discoideum

When aggregating amoebas of the cellular slime mold Dictyostelium discoideum are disaggregated and morphogenesis is reinitiated, the amoebas will reaggregate in less than $\text{1}\text{10}\text{th}$ the original time. When aggregating amoebas are disaggregated and resuspended either in full nutrient medium or in buffered salts solution containing dextrose, they retain this developmentally acquired capacity to rapidly reaggregate for approximately 1 hr and then lose it completely in a synchronous and discrete step which we have referred to as the “erasure event.” In this report, it is demonstrated that micromolar concentrations of cAMP completely block this transition from the developmental to vegetative state, and that other cyclic nucleotides also inhibit it, but they do so at 20-fold higher concentrations. Neither the hydrolysis products of cAMP nor the vegetative chemoattractant folic acid inhibit dedifferentiation at concentrations as high as 10^?3M, demonstrating a specificity for cyclic nucleotides and cAMP in particular. The addition of cAMP at any time during the lag period preceding the erasure event inhibits it and addition immediately after the erasure event reverses it. Since cAMP may inhibit the transition from the developmental to vegetative state intracellularly or extracellularly, we have also examined the intracellular concentration of cAMP and the levels of cAMP binding sites on the cell surface during the erasure process. Evidence is presented that the majority of cAMP binding sites on the cell surface are not necessary for the inhibition of erasure by cAMP. The results of these latter studies are discussed in terms of alternative models for the involvement of cAMP in the transition from the developing to vegetative state.     

Can species‐specific prey responses to chemical cues explain prey susceptibility to predation?

The perception of danger represents an essential ability of prey for gaining an informational advantage over their natural enemies. Especially in complex environments or at night, animals strongly rely on chemoreception to avoid predators. The ability to recognize danger by chemical cues and subsequent adaptive responses to predation threats should generally increase prey survival. Recent findings suggest that European catfish (Silurus glanis) introduction induce changes in fish community and we tested whether the direction of change can be attributed to differences in chemical cue perception. We tested behavioral response to chemical cues using three species of freshwater fish common in European water: rudd (Scardinius erythrophthalmus), roach (Rutilus rutilus), and perch (Perca fluviatilis). Further, we conducted a prey selectivity experiment to evaluate the prey preferences of the European catfish. Roach exhibited the strongest reaction to chemical cues, rudd decreased use of refuge and perch did not alter any behavior in the experiment. These findings suggest that chemical cue perception might be behind community data change and we encourage collecting more community data of tested prey species before and after European catfish introduction to test the hypothesis. We conclude that used prey species can be used as a model species to verify whether chemical cue perception enhances prey survival.