LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFAR covers the largely unexplored low-frequency range from 10-240 MHz and provides a number of unique observing capabilities. Spreading out from a core located near the village of Exloo in the northeast of the Netherlands, a total of 40 LOFAR stations are nearing completion. A further five stations have been deployed throughout Germany, and one station has been built in each of France, Sweden, and the UK. Digital beam-forming techniques make the LOFAR system agile and allow for rapid repointing of the telescope as well as the potential for multiple simultaneous observations. With its dense core array and long interferometric baselines, LOFAR achieves unparalleled sensitivity and angular resolution in the low-frequency radio regime. The LOFAR facilities are jointly operated by the International LOFAR Telescope (ILT) foundation, as an observatory open to the global astronomical community. LOFAR is one of the first radio observatories to feature automated processing pipelines to deliver fully calibrated science products to its user community. LOFAR's new capabilities, techniques and modus operandi make it an important pathfinder for the Square Kilometre Array (SKA). We give an overview of the LOFAR instrument, its major hardware and software components, and the core science objectives that have driven its design. In addition, we present a selection of new results from the commissioning phase of this new radio observatory.

Context. M 87 is a giant elliptical galaxy located in the centre of the Virgo cluster, which harbours a supermassive black hole of mass 6.4 × 10 9 M , whose activity is responsible for the extended (80 kpc) radio lobes that surround the galaxy. The energy generated by matter falling onto the central black hole is ejected and transferred to the intra-cluster medium via a relativistic jet and morphologically complex systems of buoyant bubbles, which rise towards the edges of the extended halo. Aims. To place constraints on past activity cycles of the active nucleus, images of M 87 were produced at low radio frequencies never explored before at these high spatial resolution and dynamic range. To disentangle different synchrotron models and place constraints on source magnetic field, age and energetics, we also performed a detailed spectral analysis of M 87 extended radio-halo. Methods. We present the first observations made with the new Low-Frequency Array (LOFAR) of M 87 at frequencies down to 20 MHz. Three observations were conducted, at 15−30 MHz, 30−77 MHz and 116−162 MHz. We used these observations together with archival data to produce a low-frequency spectral index map and to perform a spectral analysis in the wide frequency range 30 MHz-10 GHz. Results. We do not find any sign of new extended emissions; on the contrary the source appears well confined by the high pressure of the intracluster medium. A continuous injection of relativistic electrons is the model that best fits our data, and provides a scenario in which the lobes are still supplied by fresh relativistic particles from the active galactic nuclei. We suggest that the discrepancy between the low-frequency radiospectral slope in the core and in the halo implies a strong adiabatic expansion of the plasma as soon as it leaves the core area. The extended halo has an equipartition magnetic field strength of 10 μG, which increases to 13 μG in the zones where the particle flows are more active. The continuous injection model for synchrotron ageing provides an age for the halo of 40 Myr, which in turn provides a jet kinetic power of 6−10 × 10 44 erg s −1 .

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When isolated rat-liver cells were incubated for 1 min at 37 "C with filipin at a concentration of 50 pM, the plasma membrane became permeable to sucrose. inulin, glycerol 3-phosphate and other low-molecular-weiglit compounds. Upon removal of the filipin and subsequent incubation of the cells at 37°C there was a gradual leakage of lactate dehydrogenase from the cells. However, the leakage of lactate dehydrogenase could be prevented for about 10 niin by including glutathione and ATP in the incubation medium.The filipin-treated cells were able to metabolize phosphorylated sugars. The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate, glucose 6-phosphate and glucose was inhibited by AMP but not by high concentrations of fructose 1,6-bisphosphate. The results indicate that filipin-treated cells can be used to study the kinetic parameters of enzymes in their macromolecular environment in situ.

1. A method is described for measuring the binding of metabolites to cytosolic proteins in situ in isolated rat-liver cells treated with filipin to render the plasma membrane permeable to compounds of low molecular weight.2. There is no binding of ATP or inorganic phosphate to cytosolic proteins, either in the presence or in the absence of Mg2+.3. Binding of ADP to cytosolic proteins occurs both in the absence and in the presence of Mg2+. The concentration of binding sites was 0.68 and 0.52 pmol/g dry weight of cells (n = 3 -4) in the absence and presence of Mg2 +, respectively.The corresponding Kd values were 320 pM and 235 pM.It has long been recognised that the amounts of metabolites present in a cell are not necessarily a measure of the thermodynamically active species of the metabolites [I -101. Cori [I] introduced the term compartmentation for this phenomenon. Three major types of compartmentation may be envisaged (see [8, 101): firstly, spatial compartmentation may occur due to the existence of permeability barriers; secondly, compartmentation may be caused by binding of metabolites to proteins [2 -81 and thirdly, compartmentation could in principle be caused by diffusion gradients [7, 81.Since in studying metabolic regulation it is of importance to have exact information on the free concentrations of metabolites, methods have been devised to overcome the problems of compartmentation. The best-known is the metabolite indicator method, which has been used effectively to determine the free NADH/NAD+ and NADPH/NADP+ ratios [2-41 (for a review see [I 11). It should be noted that this method gives no information on the extent of binding of metabolites; this information can be obtained by direct measurement. Biicher and Sies [8], for instance, determined the NADH-binding capacity of the cytosolic proteins by Sephadex G-50 column chromatography of an isolated rat-liver cytosol fraction. However, the binding properties of proteins in a dilute solution may differ from those in the intact cell where protein-protein interactions may play a role.We have recently described a procedure for the preparation of rat-liver cells, the plasma membranes of which were rendered permeable to low molecular weight compounds by treatment with filipin whereas cytosolic proteins rcmaincd in situ [12] (see also Lardy et al. [13]). In the present study we have used this preparation to determine the binding of ATP, ADP and phosphate to cytosolic proteins in rat-liver cells. Abbreviation. Mops, morpholinepropanesulphonic acidEnzyme. Lactate dehydrogenase (EC 1.1.1 27) MATERIALS AND METHODS Isolation of Rut-Liver Cells arid Preparation of Filipiii-Treated CellsRat-liver parenchymal cells were isolated from the livers of 24-h-starved male Wistar rats (200-300 g) using a modification [12] of the method of Berry and Friend [14]. Viability was checked by the Trypan blue exclusion method; at least 90 "/, of the cells excluded the dye.Filipin-treated cells were prepared exactly as described in [12]. They were finally suspended in a standard ...