P. Kohler

APEX: current status of the airborne dispersive pushbroom imaging spectrometer

Over the past few years, a joint Swiss/Belgium ESA initiative resulted in a project to build a precursor mission of future spaceborne imaging spectrometers, namely APEX (Airborne Prism Experiment). APEX is designed to be an airborne dispersive pushbroom imaging spectrometer operating in the solar reflected wavelength range between 4000 and 2500 nm. The system is optimized for land applications including limnology, snow, and soil, amongst others. The instrument is optimized with various steps taken to allow for absolute calibrated radiance measurements. This includes the use of a pre- and post-data acquisition internal calibration facility as well as a laboratory calibration and a performance model serving as a stable reference. The instrument is currently in its breadboarding phase, including some new results with respect to detector development and design optimization for imaging spectrometers. In the same APEX framework, a complete processing and archiving facility (PAF) is developed. The PAF not only includes imaging spectrometer data processing up to physical units, but also geometric and atmospheric correction for each scene, as well as calibration data input. The PAF software includes an Internet based web-server and provides interfaces to data users as well as instrument operators and programmers. The software design, the tools and its life cycle are discussed as well.

New Aspects on the Formation and Analysis of Acrylamide

The effectiveness of different compounds in the generation of acrylamide (AA) from asparagine, was determined by reacting asparagine with mono-, di- and polysaccharides, as well as four different oxo-compounds known to be involved in carbohydrate metabolism/degradation. Quantitation of AA formed either under aqueous conditions or in low water model systems revealed glucose and 2-oxopropionic acid as the most effective compounds in AA generation, when reacted in model systems with a low water content (about 1 mol-% yield). Interestingly, heating of asparagine in the presence of 2-oxopropionic acid generated quite high amounts of 3-aminopropionamide (3-APA), which itself effectively generated AA upon heating in aqueous solution, as well as in low water systems. Because this is the first report on amounts of 3-APA generated by Maillard-type reactions, the general role of 3-APA as key intermediate in AA formation is discussed in detail. In addition, first results on the development and application of an HPLC/fluorescence method for AA quantitation are presented.

Isoprenoid biosynthesis in plants - 2C-methyl-D-erythritol-4-phosphate synthase (IspC protein) of Arabidopsis thaliana.

The ispC gene of Arabidopsis thaliana was expressed in pseudomature form without the putative plastid‐targeting sequence in a recombinant Escherichia coli strain. The recombinant protein was purified by affinity chromatography and was shown to catalyze the formation of 2C‐methyl‐d‐erythritol 4‐phosphate from 1‐deoxy‐d‐xylulose 5‐phosphate at a rate of 5.6 µmol·min−1·mg−1 (kcat 4.4 s−1). The Michaelis constants for 1‐deoxy‐d‐xylulose 5‐phosphate and the cosubstrate NADPH are 132 and 30 µm, respectively. The enzyme has an absolute requirement for divalent metal ions, preferably Mn2+ and Mg2+, and is inhibited by fosmidomycin with a Ki of 85 nm. The pH optimum is 8.0. NADH can substitute for NADPH, albeit at a low rate (14% as compared to NADPH). The enzyme catalyzes the reverse reaction at a rate of 2.1 µmol·min‐1·mg‐1.

Evolution of vitamin B2 biosynthesis: riboflavin synthase of Arabidopsis thaliana and its inhibition by riboflavin.

Abstract A synthetic gene specifying the catalytic domain of the Arabidopsis thaliana riboflavin synthase was expressed with high efficiency in a recombinant Escherichia coli strain. The recombinant pseudomature protein was shown to convert 6,7-dimethyl-8-ribityllumazine into riboflavin at a rate of 0.027 s−1 at 25°C. The protein sediments at a rate of 3.9 S. Sedimentation equilibrium analysis afforded a molecular mass of 67.5 kDa, indicating a homotrimeric structure, analogous to the riboflavin synthases of Eubacteria and fungi. The protein binds its product riboflavin with relatively high affinity (K d=1.1 μM). Product inhibition results in a characteristic sigmoidal velocity versus substrate concentration relationship. Characterization of the enzyme/product complex by circular dichroism and UV absorbance spectroscopy revealed a shift of the absorption maxima of riboflavin from 370 and 445 to 399 and 465 nm, respectively. Complete or partial sequences for riboflavin synthase orthologs were analyzed from 11 plant species. In each case for which the complete plant gene sequence was available, the catalytic domain was preceded by a sequence of 1–72 amino acid residues believed to function as plastid targeting signals. Comparison of all available riboflavin synthase sequences indicates that hypothetical gene duplication conducive to the two-domain architecture occurred very early in evolution.

Status of the airborne dispersive pushbroom imaging spectrometer APEX (Airborne Prism Experiment)

Over the past few years, a joint Swiss/Belgian initiative resulted in a project to build a new generation airborne imaging spectrometer, namely APEX (Airborne Prism Experiment) under the ESA funding scheme named PRODEX. APEX is designed to be a dispersive pushbroom imaging spectrometer operating in the solar reflected wavelength range between 400 and 2500 nm. The spectral resolution is designed to be better than 10 nm in the SWIR and 5 nm in VIS/NIR range of the spectrum. The total FOV is on the order of /spl plusmn/14/spl deg/, recording 1000 pixels across track, and max. 300 spectral bands simultaneously. The final radiance data products are well characterized and calibrated to be traceable to absolute standards. APEX is subdivided into an industrial team responsible for the optical instrument, the calibration home base, and the detectors, and a science and operational team, responsible for the processing and archiving of the imaging spectrometer data, as well as its operation. APEX is in its design phase with partial breadboarding activities and will be operationally available to the user community in the year 2005.

Chorionic Gonadotropin Synthesis and Gene Assignment in Human: Mouse Hybrid Cells

Chorionic gonadotropin (hCG) is a hormone of special interest in the field of human tumor biology. This glycoprotein hormone is secreted in vast quantities by the syncytiotrophoblast of the placenta during normal pregnancy. However, ectopic or inappropriate secretion of either or both subunits of hCG is a relatively common occurrence in tumors of non-placental origin1–4. Clearly, an appreciation of the control of hCG synthesis would be useful in determining the reason for the high frequency of ectopic synthesis of this tumor marker.

Overview of Pituitary Tumor Treatment

Major advances in the diagnostic and therapeutic approaches to pituitary tumors have occurred over the past two decades. As a result of the increased capacity to detect and treat pituitary microadenomas, the goals of treatment are now often different. Several years ago, the diagnosis of pituitary tumor was most often made in patients over 40 years of age.1 Frequently, the presenting complaints include visual defects, indicating relatively large tumors.2 In addition, most pituitary tumors were believed to be nonfunctional because (1) no hypersecretory syndrome was clearly identified in approximately 75% of patients and (2) on histological examination, the tumor cells showed no specific chromophilic hormone granules. The therapeutic goal in patients with these so-called “chromophobe adenomas” was often to prevent expansion or control tumor growth and avoid the visual and endocrine deficiencies caused by the mass effect of the tumor. Total resection of the tumor was not necessarily recommended because of the high incidence of complete pituitary dysfunction and fatality.3 Therapy for these tumors was usually either trans-frontal surgery,1 external irradiation,4 or a combination of both.5