Porous polymers for fixed bed adsorption of aroma compounds in fermentation processes

Summary Deionized water as well as simulated and genuine fermentation media, which contained varying concentrations of benzaldehyde and 4-decanolide, were used to investigate the applicability of selected styrene-divinylbenzene resins for low pressure downflow adsorption of aroma compounds in a fixed bed. The effects of flow rate and matrix on the respective breakthrough curve slopes were examined using the LUB-and the MTZ-model.     

The function of mitochondria-rich cells (chloride cells) in teleost gills

Summary The CCs are the site of Cl^– transport in teleosts in sea water. The gills of freshwater teleosts contain at least two types of mitochondria-rich cell, the type and the type (Pisam and Rambourg, 1991). During seawater acclimation, the cells vanish and the cells are transformed and proliferate, and accessory cells appear in addition. This gives rise to the question of the function of cells in fish living in fresh water.According to the studies reviewed here, although they deal only with extrabranchial epithelia, the majority of evidence indicates that CCs (or MRCs) function as sites of active Ca²⁺ transport in freshwater teleosts. Moreover, some experimental results suggest that CCs are the Cl^– uptake site in freshwater teleosts. The main problem in characterizing the CC function is that they have not yet been adequately described from the biochemical standpoint. This applies particularly to their metabolic pattern and the composition of their apical and basolateral membranes, including their integrated proteins and cell-cell junctions.Experiments with organ tissue cultures such as gill organ cultures from Oncorhynchus mykiss (McCormick and Bern, 1989) and opercular membrane cultures from Oreochromis mossambicus (McCormick, 1990) will almost certainly yield important results. Primary cell cultures of CCs would be even better for characterizing CCs. Such a cell culture of rainbow trout respiratory cells has already been established (Pärt et al., 1993).     

Nitrate reductase deficient cell lines from haploid protoplast cultures ofNicotiana plumbaginifolia

Summary Nitrate reductase deficient (NR^-) cell lines were selected indirectly by their resistance to 40 mM chlorate in protoplast cultures of haploidNicotiana plumbaginifolia. Frequency of the chlorate resistant clones was 5.8×10^-5 in non-mutagenized cultures, which could be increased up to 25 times by treatment with N-ethyl-N-nitrosourea (NEU) or gamma irradiation.Out of 136 chlorate resistant clones 29 were fully deficient in nitrate reductase. The rest of the clones contained decreased or normal levels of NR activity (91 and 16 clones, respectively).Further characterization was carried out in 9 clones which were fully deficient in NR and in 2 clones containing resisdual (0–5%) NR activity. The clones were tentatively classified as defective in the apoenzyme (7 clones including the 2 with residual NR activity) or the cofactor (4 clones) of NR by the xanthine dehydrogenase activity and in vitro enzyme complementation. The cofactor defectives could be further classified into two groups. In one of these (2 clones) the NR activity could be partially restored by unphysiologically high (0.2–1 mM) molybdate in the culture medium. The other two are new types which have not been described in flowering plants.Plant regeneration was obtained only in the clones which contained residual NR activity.     

Structural variability in the genome of phage ?H of Halobacterium halobium

Summary The partially circularly permuted, terminally redundant structure of the DNA of phage H has been confirmed by a cleavage map for the restriction enzymes PstI, ClaI, BglII, HindIII, and, partially, BamHI.Six variants of phage H have been isolated from 71 single plaques. Their genomes differ by several insertions, a deletion, and an inversion of a DNA segment with a minimal length of 11 kb. The inversion occurs with high frequency in variants carrying at the flanks of the invertible DNA in verted repeats of a 1.8 kb DNA element which shares sequence homology with the DNA of H. halobium and may be involved in the extreme variability of its genome.     

Inhibition of yeast tRNATrp aminoacylation by 4-methyltryptophan

The effect of the tryptophan analogue 4-methyltryptophan in Saccharomyces cerevisiae has been investigated. 4-Methyltryptophan inhibits the aminoacylation of tryptophan specific transfer ribonucleic acid (tRNA^Trp). The mode of inhibition is competitive and the analogue is not charged onto tRNA^Trp. Thus 4-methyltryptophan application depletes the cells from charged tRNA^Trp. As a consequence cell growth and protein synthesis are strongly reduced. 4-Methyltryptophan is degraded efficiently in culture media inoculated with the wild type strain; the effects of 4-methyltryptophan were therefore found to be transient.     

Restriction analysis of the Streptomyces glaucescens genome by agarose gel electrophoresis

A method for the analysis of total DNA of Streptomyces glaucescens is described. The relevant steps are (a) extraction and purification of DNA, (b) restriction of DNA samples with type II restriction enzymes, (c) one dimensional separation of restriction fragments by agarose gel electrophoresis. A typical banding pattern was obtained for each wild type strain, independant of growth conditions or age of the culture. Mutant strains exhibited in most cases the same banding pattern as the parent wild type strain. Only in one specific mutant class a fragment of about 9 megadalton was missing.     

Rate-controlling steps of oxidative phosphorylation in rat liver mitochondria. A synoptic approach of model and experiment

The contribution of different steps to the control of oxidative phosphorylation in isolated rat liver mitochondria was investigated by a combination of experiments and computer simulations. The parameters of the mathematical model of phosphorylating mitochondria were derived from experimental data. The model correctly describes the competition between ATP utilization inside and outside mitochondria for the ATP generated in mitochondria. On the basis of the good agreement between experiments and simulations, the contribution of different steps to the control of respiration was estimated by computing their control strengths, i.e., the influence of their activities on the rate of respiration. The rate-controlling influences vary depending on the load of oxidative phosphorylation. The predominant steps are: in the fully active state (State 3) — the hydrogen supply to the respiratory chain; in the resting state (State 4) — the proton leak of the mitochondrial inner membrane; in states of non-maximum ATP export — the adenine nucleotide translocator. Titrations of respiration with phenylsuccinate, antimycin, oligomycin and carboxyatractyloside completely support these conclusions.