Electron transfer proteins of the purple phototrophic bacterium, Rhodopseudomonas rutila.

The soluble electron transfer protein content of Rhodopseudomonas rutila was found to consist of two basic cytochromes and a (4Fe-4S) ferredoxin. Cytochrome c' was easily identified by its characteristic high spin absorption spectra. The native molecular weight is 29,000 and the subunit is 14,000. Cytochrome c-550 has low spin absorption spectra and a high redox potential (376 mV) typical of cytochromes c2. The molecular weight is about 14,000. The ferredoxin is apparently a dimer (43,000) of approximately 18,000 Da subunits. There are 1.3 to 1.5 iron-sulfur clusters per monomer of 18- to 21-kDa protein. The N-terminal amino acid sequence is like the (7Fe-8S) ferredoxins of Rhodobacter capsulatus and Azotobacter vinelandii. Remarkably, there are only 2 or 3 out of 25 amino acid substitutions. Difference absorption spectra of Rps. rutila membranes indicate that there is not tetraheme reaction center cytochrome c, such as is characteristic of Rps. viridis. However, there are a high potential cytochrome c and a low potential cytochrome b in the membrane, which are suggestive of a cytochrome bc1 complex. Rps. rutila is most similar to Rps. palustris in microbiological properties, yet it does not have the cytochromes c-556, c-554, and c-551 in addition to c2 and c', which are characteristic of Rps. palustris. Furthermore, the Rps. rutila cytochrome c' is dimeric, whereas the same protein from Rps. palustris is the only one known to be monomeric. The cytochrome pattern is more like that of Rhodospirillum rubrum and Rb. capsulatus, which are apparently only able to make cytochromes c2 and c'.     

Adenylylation state of glutamine synthetase and permeability properties of Pseudomonas fluorescens

The state of adenylylation, n, of glutamine synthetase (GS) in Pseudomonas fluorescens has been determined as a function of growth conditions. Compared to the behavior of Escherichia coli, atypical responses to either carbon or nitrogen starvation were observed when P. fluorescens was grown with either succinate, malate, or fumarate as the sole source of carbon and energy. Under conditions of carbon starvation (high NH4+, low dicarboxylic acid substrate), the value of n falls rapidly from 10 to 1.0 during prolonged incubation in the stationary phase, whereas the value of n is unexpectedly high (ca. 10) in extracts of nitrogen-starved cells. These abnormal responses are attributable to particular permeability properties of P. fluorescens cells compared to E. coli. The unusual changes in nitrogen-starved cells are related to the release of alpha-ketoglutarate by such cells during incubation or washing procedures. These changes can be prevented by the addition of cetyltrimethylammonium bromide (CTAB) to the cultures 5 min prior to harvesting the cells, or by freezing the cell pellets just after centrifugation and sonication within 3 min of suspension in buffer, or by suspending freshly harvested cells in buffer containing alpha-ketoglutarate and orthophosphate (i.e., effectors that favor deadenylylation of glutamine synthetase). The abnormal changes which occur during carbon starvation in the presence of excess NH4+ can be prevented by addition of ATP and glutamine to the buffer in which the freshly harvested cells are suspended prior to sonication. The results suggest that during the stationary phase of growth on succinate, fumarate, or malate (but not on glucose), the cellular membrane becomes permeable to small molecules that regulate the adenylylation cascade, and indeed, it was observed that such whole cells expressed, without any chemical or physical treatment, more than 50% of the glutamine synthetase activity they contained. Such cells may be useful in studies to examine the effects of multiple metabolites on the regulation of glutamine synthetase adenylylation in situ.     

Some facts concerning the nature and formation of axial core structures in spermatids of Gryllus domesticus

Examination of living spermatid nuclei of Gryllus domesticus has revealed the presence of the same structures, the X chromosome, the round body and the axial core structures, which have been described from electron microscopic observations. The outer ribbons of the axial core structures and the round body are composed of 100 Å fibres indiscernible from and often continuous with the fibres composing the X chromosome. That the outer ribbons of the axial core structures and the round body are chromosomal is further substantiated by the results of cytochemical examinations of formaldehyde fixed material which show that the axial core structures and the round body contain RNA, DNA and basic protein. Neither acetic acid-ethanol nor cold ethanol fixation preserve the round body and the axial core structures suggesting that a protein may be responsible for maintenance of the central core structure. The central core structures are always found in close association with condensed chromatin in regions where the chromosome elements are about 1000 Å apart, suggesting that the relative state of condensation of the chromatin and the spacial relationship between condensed regions may be two of the chief factors concerned in central core formation. Maintainance of the condensed state of the chromatin, however, may in turn depend upon central core integrity.Herrn Prof. J. Seiler zu seinem 80. Geburtstag gewidmet.     

The sigma receptor as a ligand-regulated auxiliary potassium channel subunit

The sigma receptor is a novel protein that mediates the modulation of ion channels by psychotropic drugs through a unique transduction mechanism depending neither on G proteins nor protein phosphorylation. The present study investigated sigma receptor signal transduction by reconstituting responses in Xenopus oocytes. Sigma receptors modulated voltage-gated K+ channels (Kv1.4 or Kv1.5) in different ways in the presence and absence of ligands. Association between Kv1.4 channels and sigma receptors was demonstrated by coimmunoprecipitation. These results indicate a novel mechanism of signal transduction dependent on protein-protein interactions. Domain accessibility experiments suggested a structure for the sigma receptor with two cytoplasmic termini and two membrane-spanning segments. The ligand-independent effects on channels suggest that sigma receptors serve as auxiliary subunits to voltage-gated K+ channels with distinct functional interactions, depending on the presence or absence of ligand.     

Development and adaptation of a multiprobe biosensor for the use in a semi-automated device for the detection of toxic algae

Worldwide monitoring programs have been launched for the observation of phytoplankton composition and especially for harmful and toxic microalgae. Several molecular methods are currently used for the identification of phytoplankton but usually require transportation of samples to specialised laboratories. For the purpose of the monitoring of toxic algae, a multiprobe chip and a semi-automated rRNA biosensor for the in-situ detection of toxic algae were developed. Different materials for the electrodes and the carrier material were tested using single-electrode sensors and sandwich hybridisation that is based on species-specific rRNA probes. Phytoplankton communities consist of different species and therefore a biosensor consisting of a multiprobe chip with an array of 16 gold electrodes for the simultaneous detection of up to 14 target species was developed. The detection of the toxic algae is based on a sandwich hybridisation and an electrochemical detection method.     

Apoptosis does not affect the vasculature of the corpus luteum of pregnancy in the rat

There has been much research into the mechanics of angiogenesis and many studies have demonstrated that newly formed vessels regress during angiogenesis. This vascular involution has been shown to involve basement membrane dissolution and endothelial cell apoptosis. The corpus luteum provides an ideal in vivo model to study physiologic angiogenesis and studies have shown that involution of newly formed vessels occurs during corpus luteum regression. However, few studies to date have investigated the role of apoptosis on the vasculature which develops during pregnancy. By the use of the TUNEL technique to detect apoptotic cells and immunohistochemistry to distinguish between endothelial cells and pericytes, this present study demonstrated that the vasculature of the corpus luteum of pregnancy in the rat does not undergo apoptosis.     

A stochastic population model for Lepidium papilliferum (Brassicaceae), a rare desert ephemeral with a persistent seed bank

Population viability analysis (PVA) is a valuable tool for rare plant conservation, but PVA for plants with persistent seed banks is difficult without reliable information on seed bank processes. We modeled the population dynamics of the Snake River Plains ephemeral Lepidium papilliferum using data from an 11-yr artificial seed bank experiment to estimate age-specific vital rates for viability loss and germination. We related variation in postgermination demographic parameters to annual variation in precipitation patterns and used these relationships to construct a stochastic population model using precipitation driver variables. This enabled us to incorporate realistic levels of environmental variability into the model. A model incorporating best estimates for parameter values resulted in a mean trajectory for seed bank size that remained essentially stable through time, although there was a measurable risk of extinction over a 100-yr period for the study population under this scenario. Doubling the annual seed viability loss rate resulted in near-certain extinction, as did increasing first-year germination to 100%, showing the importance of the persistent seed bank. Interestingly, increasing environmental variance substantially decreased the risk of extinction, presumably because this plant relies on extremely good years to restock the persistent seed bank, while extremely bad years have little impact. If every year were average in this desert environment, the species could not persist. Simulated effects of livestock trampling resulted in greatly increased extinction risk, even over time frames as short as 15 years.