Light distribution in a novel photobioreactor – modelling for optimization

The paper reports a novel photobioreactor developed to achievehomogeneous and flexible illumination inside the reactor. This is toovercome the problem of studying kinetics in standard photobioreactors,which are characterized by strong light gradients and light fluxes that cannotbe controlled. The reactor is used for the study of microalgal kinetics formodelling purposes.The new reactor combines the advantages of a stirred reactor(homogeneity) and a plate reactor (short path length). The light inputsystem consists of an external light source, a fibre-optical ring-light and alight emitting tube. Light is generated in a light source arranged externallyand directed into the reactor using optical fibres. The fibres are spread ina ring-light to provide a uniform illumination in the concentrically arrangedcylinder. Any focusable light source can be applied; by using a shuttermodule, light fluctuations can be generated in a wide range of frequencies.In order to change the light quality, spectral filters are placed between thelamp and the optical fibre.A model based approach was used to optimize the illumination: lightdistribution was calculated employing a Monte-Carlo simulation. Lightemission characteristics, reflection, refraction, scattering in the suspensionand on rough surfaces were studied numerically. Propositions were derivedhow to optimize the reactor, e.g. now to achieve higher light intensities anda more uniform illumination. Finally, mean photon flux densities of 100± 15 mol m^-1 s^-1 were achieved at theilluminated surface.The simulation results revealed that the light distribution at constantbiomass concentration is mainly determined by the geometrical parametersof the lightening device mentioned above and that any simplifications leadto serious misinterpretations.     

Expression of differentiated functions in dexamethasone-resistant hepatoma cells

Abstract. The expression of liver-specific functions of different dexamethasone-resistant variants derived from a well-differentiated dexamethasone-sensitive Reuber H35 rat hepatoma cell line (Faza 967) was examined during long-term cultivation. The dexamethasone-sensitive Faza 967 cells are characterized by the activity of tyrosine aminotransferase (TAT) and gluconeogenic enzymes, secretion of serum albumin, and the presence of liver isozymes of alcohol dehydrogenase (L-ADH), aldolase (aldolase-B), and five isoenzymes of lactate dehydrogenase (LDH). The hormone-resistant cells undergo a very dramatic change in expression of most liver-specific functions (dedifferentiation) during long-term culture, in contrast to the sensitive cells in which only certain functions (TAT activity, inducibility, and synthesis of serum albumin) exhibit considerable changes. The hormone-dependent growth sensitivity and the expression of other differentiated functions is not controlled in coordinated way in Faza 967 cells. The time course of the expression of liver-specific functions shows that the cells are resistant before they became 'dedifferentiated', i.e., loss of these liver-specific functions is not a prerequisite of the establishment of the hormone-resistant state.     

Morphine-like analgesic effect of a pituitary hormone, β-lipotropin

The analgesic effect f β-lipotropin /β -LPH/ and its fragments administered intracerebroventricularly /ICV/ to rats was studied. β -LPH proved to be a specific, morphine-like analgesic possesing 2.2 times weaker analgesic potency than morphine, calculated on molar base. Tryptic digest of β -LPH or smaller fragments of the hormone /LPH-/61 2 65/-eptide and LPH-/61–69/-peptide/ were devoid of significant analgesic activity. The in vivo results appeared to be in contrast to those previously obtained in longitudinal muscle strip of guinea-pig ileum, in vitro. A tentative explanation of this apparent contradiction is also given.     

Intergeneric gene transfer mediated by plant protoplast fusion

Summary In attempts at somatic transfer of plant genomes of reduced size, X-irradiated leaf protoplasts of parsley (Petroselinum hortense, 2n=22) were fused with cell culture protoplasts of a nuclear albino mutant of carrot (Daucus carota, 2n=18). Introduction of genes from the irradiated parsley nuclei into the carrot genome was shown by the correction of the albino defect and by the appearance of parsley isoenzymes in selected green tissues and plants. The cytological studies provided information on significant deviation from the amphidiploid chromosome number. The high frequency of cells with 2n=19, 2n=38 and regeneration of plants with 2n=19 chromosomes can indicate that the elimination of parsley chromosomes is incomplete. A correlation was found between the lethality of selected tissues and differentiated or undifferentiated stages of the cells.     

A quantitative assay to measure chromosome stability in Schizosaccharomyces pombe

Summary The fidelity of mitotic chromosome transmission in Schizosaccharomyces pombe was estimated quantitatively by using cycloheximide resistance as a means to select cells that had undergone chromosome loss or nondisjunction. We aimed to investigate the connection between recombination and mitotic chromosome stability. A number of mutants defective in mitotic recombination such as cdc17-L16, rec59-72, and rec50-25 were tested and in these an approximately ten fold elevation of mitotic haploidization rate was found compared with controls. Our data suggest that recombination is important in controlling the maintenance of chromosomes during mitosis.     

Solution structure of the soluble receptor for advanced glycation end products (sRAGE)

The receptor for advanced glycation end products (RAGE) is a multiligand cell surface receptor involved in various human diseases, as it binds to numerous molecules and proteins that modulate the activity of other proteins. Elucidating the three-dimensional structure of this receptor is therefore most important for understanding its function during activation and cellular signaling. The major alternative splice product of RAGE comprises its extracellular region that occurs as a soluble protein (sRAGE). Although the structures of sRAGE domains were available, their assembly into the functional full-length protein remained unknown. We observed that the protein has concentration-dependent oligomerization behavior, and this is also mediated by the presence of Ca(2+) ions. Moreover, using synchrotron small angle x-ray scattering, the solution structure of human sRAGE was determined in the monomeric and dimeric forms. The model for the monomer displays a J-like shape, whereas the dimer is formed through the association of the two N-terminal domains and has an elongated structure. These results provide insights into the assembly of the RAGE homodimer, which is essential for signal transduction, and the sRAGE:RAGE heterodimer that leads to blockage of the receptor signaling, paving the way for the design of therapeutic strategies for a large number of different pathologies.