A stereoselective cobalt-containing nitrile hydratase

Nitrile hydratase from Pseudomonas putida NRRL-18668 has been purified and characterized. The purified enzyme catalyzes the hydration of 2(S)-(4'-chlorophenyl)-3-methylbutyronitrile at least fifty times faster than that of 2(R)-(4'-chlorophenyl)-3-methylbutyronitrile. This enzyme is a member of the class of nitrile hydratase that contains cobalt. Visible absorption and CD spectra suggest the cobalt exists as a non-corrin low-spin Co3+ ion in a tetragonally-distorted octahedral ligand field. Chemical reduction of the native enzyme results in a species with the EPR signature of a low-spin Co2+ complex. Like the other cobalt-containing nitrile hydratases, this enzyme is relatively stable, maintaining its activity below 35 degrees C, and it shows a broad activity optimum between pH 7.2 and 7.8. The structural genes for this enzyme have been cloned and sequenced. The deduced amino acid sequences for the alpha and beta subunits show 48-63% and 35-41% homology, respectively, to other sequenced nitrile hydratases. In particular, the cysteine residues in the alpha subunit that have been suggested to coordinate the metal ion in the iron-containing nitrile hydratases [Brennan, B. A., Cummings, J. G., Chase, D. B., Turner, I. M., Jr., & Nelson, M. J. (1996) Biochemistry 35, 10068-10077] are conserved in this enzyme, suggesting that this nitrile hydratase, like the enzyme from Rhodococcus rhodochrous J1, is a member of a newly described class of metalloenzymes with Co3+-thiolate ligation [Brennan, B. A., Alms, G., Nelson, M. J., Durney, L. T., & Scarrow, R. C. (1996) J. Am. Chem. Soc. 118, 9194-9195].     

Implantable biomedical microsystems for neural prostheses.

In the following article, the technologies to fabricate polyimide-based thin and flexible substrates with monolithically integrated electrode arrays and printed circuit boards (PCB) for hybrid electronic assemblies as well as an assembling technique that connects bare electronic dice with flexible PCBs are presented. The concept of modular, flexible biomedical microsystems as neural prostheses is introduced in general and described in detail in three examples. A cuff electrode with integrated multiplexer circuitry and standard implantable cables represents the combination of microtechnology with precision mechanics; a sieve electrode used as an implant in peripheral nerve regeneration studies demonstrates the next level of integration density but still uses a cable connection; and last, joint effort to fabricate the demonstrator of a vision prosthesis that is completely implantable in the eye with a wireless link for energy supply and data transmission is presented. System design, hybrid assembling technology, and flexible multilayer encapsulation using parylene and silicone rubber are the key components for creating a new generation of neural prostheses for complex and challenging new applications.     

Enterprise Social Networks as Digital Infrastructures - Understanding the Utilitarian Value of Social Media at the Workplace

ABSTRACT

In this study, we first show that while both the perceived usefulness and perceived enjoyment of enterprise social networks impact employees’ intentions for continuous participation, the utilitarian value significantly outpaces its hedonic value. Second, we prove that the network’s utilitarian value is constituted by its digital infrastructure characteristics: versatility, adaptability, interconnectedness and invisibility-in-use. The study is set within a software engineering company and bases on quantitative survey research, applying partial least squares structural equation modeling.     

Mechanistic aspects of the de-novo synthesis of PCDD/PCDF on model mixtures and MSWI fly ashes using amorphous 12C- and 13C-labeled carbon

The formation of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) from amorphous 12C- and 13C-labeled carbon was studied on model mixtures and real fly ashes. PCDD/F can either be formed directly (de-novo) from carbon already present in fly ash or step-by-step via condensation of two aromatic rings. Using model mixtures containing 12C- and 13C-labeled carbon in various ratios we observed the formation of the following compound classes: 12C6-PCPh, -PCBz, 13C6-PCPh, -PCBz, 12C12-PCDD/ F, 13C12-PCDD/F, and 12C6 13C6-PCDD/F. By examining the fraction of the mixed PCDD/F (one of the two aromatic ring is composed solely of 12C-atoms while the other contains only 13C-atoms) in the total concentration of PCDD/F, conclusions on the formation of these three ring structures are possible. From the experimental results, it can be concluded that both reaction mechanisms are operative in the formation of PCDD/F from carbon. On fly ashes approximately half of the total amount of PCDD is formed via condensation of de-novo created C6-precursors e.g. chlorophenols, while the remainder is directly released (de-novo) from the carbon i.e., formed from a related C12-structure. However, the condensation of intermediate aromatic C6-precursors is of minor importance in the formation of PCDF. With increasing temperature the relative amount of the 12C6 13C6-PCDD formed by condensation decreases due to the faster evaporation of chlorophenols. At a constant reaction temperature, the ratio of both reaction pathways is hardly influenced by reaction time. In experiments with fly ashes doped with 13C-labeled carbon, this carbon isotope shows a similar reactivity as the native carbon present on the fly ash. Thus, the used amorphous carbons are suitable models for this investigation.     

Manufacturing, assembling and packaging of miniaturized neural implants

Implantable medical devices to interface technical aids with muscles, peripheral nerves, and the brain have been developed for many applications over the last decades. They have been investigated in fundamental neuroscientific studies and some of them have been transferred into clinical practice in diagnosis, therapy and rehabilitation, respectively. Success stories of these implants have been written with help of precision mechanics manufacturing techniques. Latest cutting edge research approaches to restore vision in blind persons and to develop an interface with the human brain as motor control interface, however, need more complex systems, larger scales of integration and higher degrees of miniaturization. Microsystems engineering offers adequate tools, methods, and materials but so far, no MEMS based active medical device has been transferred into clinical practice. Here, different designs, manufacturing technologies and packaging paradigms will be presented and assessed in close relation to the envisioned neuroscientific or medical application.     

Fast and precise positioning of single cells on planar electrodesubstrates

For cell biosensors and for studying neural networks using planar electrode substrates, a suitable technique for positioning single cells on electrodes was needed. We reported a new method for fast and efficient positioning of single cells on ring electrodes by controlled suction through holes. We described the microfabrication of electrode substrates with microholes and the cell positioning procedure. L929 cells and Neuro 2A cells could be positioned in parallel without cell damage.     

Some uncollected writings reprinted from early publications

Abstract

It is rather odd to write about amateur photography in Germany, when such a thing hardly exists; and still I venture to say a few words about its future, as it is almost certain that Berlin, Germany's centre for science, has given it an impetus, which promises to bring forth a host of well-trained workers. Thanks to the munificence of the city, which devoted upwards of £1,000,000 to the purpose, a new technical high school was erected and opened about two years ago. The building is a grand work of architectural art, unsurpassed by any educational institution on the face of the globe, both in exterior and interior beauty, and practicality. It is of enormous dimensions, and the 800 or 900 students who now occupy it are quite lost within its walls, as the building can accommodate 2000 or more.     

Quality assurance in inpatient treatment of depression. Aspects of quality monitoring and external quality assurance exemplified by a pilot project of inpatient treatment of depression]

An apparent species-specific relatedness of SIVagm suggests a coevolution with their natural hosts. However, the exact species or subspecies classification of African green monkeys, AGM, is uncertain because current classification schemes rely on phenotype markers, while more definitive genetic data are lacking. In this study, the CD4 protein involved in tissue type recognition was genetically cloned and sequenced from PBMC RNA from all AGM species, including Barbados green monkeys (BGM). Phylogenetic trees were constructed that also included genomic CD4 nucleotide sequences from patas, sooty mangabeys, rhesus and pig-tail macaques, chimpanzees, and humans. Chimpanzees and humans consistently clustered together. Monkeys within the Cercopithecus genus formed a separate cluster which included pata monkeys, supporting its grouping as a member of Cercopithecus. Surprisingly, sooty mangabeys were genetically more closely related to Asian macaques than to other African species, which might explain why macaques are more susceptible to infection by the SIVsm group than to infection by SIVagm or HIV-1 and why patas, on the other hand, are highly susceptible to SIVagm infection. Based on CD4 genetic data, tantalus, vervets, grivets, and sabaeus formed separate subgroups with BGM grouping closely with vervets. The branching order of the AGM species was related to that of their respective SIVagm env sequences. The study suggests a strong correlation between CD4 phylogeny and the susceptibility of the host species to infection by a specific lentivirus and supports the assumption of a coevolution of SIVagm and AGM. CD4 sequencing is suggested as a relevant method for genetic determination of primate species.     

Serum concentrations of thyroid hormones in patients with nonseasonal affective disorders during treatment with bright and dim light

Serum concentrations of thyroxine (T4), triiodothyronine (T3), and thyrotropine were measured in 34 patients with nonseasonal affective disorders before and after 1 week of light treatment. Nineteen of these patients received bright white light (2500 lx) and 15 dim red light (50 lx) for 2 hours daily in the mornings over a 1-week period. Slight but significant reductions in the rating scores for the depressive symptomatology were found for both the bright-and dim-light groups, but there were no significant differences between the two groups. The improvement is thus most likely a placebo effect. Surprisingly, the small changes in the severity of the depressive symptoms in the group as a whole were significantly correlated to the changes in the serum levels of T4 during the weeks of bright- and dim-light treatment, respectively. The more a patient improved, the further his or her T4 level fell and vice versa. The fluctuations in the concentrations of T4 during light treatment were significantly greater in the depressed patients than in a group of 12 healthy controls who also received bright or dim light, whereas the changes in T3 were significantly smaller than those of the healthy controls. The pronounced fluctuations in T4 levels were probably not secondary to changes in mood. Rather, they are likely to reflect changes in tissue (intracellular) metabolism of T4, which may be involved in the mechanisms underlying the fluctuations in mood in these patients.