Detection of Formaldehyde Towards the Extreme Carbon Star IRC+10216

We report the detection of H2CO (formaldehyde) around the carbon-rich AGB star, IRC+10216. We find a fractional abundance with respect to molecular hydrogen of x(H2CO)= (1.3 {+1.5}{-0.8}) x 10^{-8}. This corresponds to a formaldehyde abundance with respect to water vapor of x(H2CO)/x(H2O)=(1.1 +/- 0.2) x 10^{-2}, in line with the formaldehyde abundances found in Solar System comets, and indicates that the putative extrasolar cometary system around IRC+10216 may have a similar chemical composition to Solar System comets. However, we also failed to detect CH3OH (methanol) around IRC+10216 and our upper limit of x(CH3OH)/x(H2O) < 7.7 x 10^{-4}, (3 sigma), indicates that methanol is substantially underabundant in IRC+10216, compared to Solar System comets. We also conclude, based on offset observations, that formaldehyde has an extended source in the envelope of IRC+10216 and may be produced by the photodissociation of a parent molecule, similar to the production mechanism for formaldehyde in Solar System comet comae. Preliminary mapping observations also indicate a possible asymmetry in the spatial distribution of formaldehyde around IRC+10216, but higher signal-to-noise observations are required to confirm this finding. This study is based on observations carried out with the IRAM 30m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). (abridged)Comment: accepted to ApJ, 45 pages, 11 figure

Pre-steady-state charge translocation in NaK-ATPase from eel electric organ

Time-resolved measurements of charge translocation and phosphorylation kinetics during the pre-steady state of the NaK-ATPase reaction cycle are presented. NaK-ATPase-containing microsomes prepared from the electric organ of Electrophorus electricus were adsorbed to planar lipid bilayers for investigation of charge translocation, while rapid acid quenching was used to study the concomitant enzymatic partial reactions involved in phosphoenzyme formation. To facilitate comparison of these data, conditions were standardized with respect to pH (6.2), ionic composition, and temperature (24 degrees C). The different phases of the current generated by the enzyme are analyzed under various conditions and compared with the kinetics of phosphoenzyme formation. The slowest time constant (tau 3-1 approximately 8 s-1 is related to the influence of the capacitive coupling of the adsorbed membrane fragments on the electrical signal. The relaxation time associated with the decaying phase of the electrical signal (tau 2-1 = 10-70 s-1 depends on ATP and caged ATP concentration. It is assigned to the ATP and caged ATP binding and exchange reaction. A kinetic model is proposed that explains the behavior of the relaxation time at different ATP and caged ATP concentrations. Control measurements with the rapid mixing technique confirm this assignment. The rising phase of the electrical signal was analyzed with a kinetic model based on a condensed Albers-Post cycle. Together with kinetic information obtained from rapid mixing studies, the analysis suggests that electroneutral ATP release, ATP and caged ATP binding, and exchange and phosphorylation are followed by a fast electrogenic E1P-->E2P transition. At 24 degrees C and pH 6.2, the rate constant for the E1P-- >E2P transition in NaK-ATPase from eel electric organ is > or = 1,000 s-1

Electrogenic and electroneutral partial reactions in Na⁺/K⁺ ATPase from eel electric organ

The generally accepted reaction scheme of the Na+/K+-ATPase is the Albers-Post cycle. It defines the reaction mechanism of the enzyme by a sequence of intermediates which are characterized by their chemical or structural properties, namely, conformation and state of phosphorylation. While much information has been accumulated about the reaction mechanism, much less is known about the transport mechanism of the Na+/K+-ATPase. An obvious strategy to address the latter problem is to correlate charge movement to the partial reactions in the Albers-Post scheme. The underlying assumption in this approach is that the charge movement reflects the movement of the transported Na+or K+ ions inside the protein