Conditions used with a continuous cultivation system to screen for d-hydantoinase-producing microorganisms

The continuous cultivation technique has been used to screen for microorganisms producing d-hydantoinase, a biocatalyst involved in the production of optically active amino acids. Pseudomonas putida strain DSM 84 was used as a model hydantoinase producer to establish selective culture conditions through the addition of various pyrimidines, dihydropyrimidines, hydantoins and 5-monosubstituted hydantoins. Thymine induced more activity than all cyclic amides tested. Addition of thymine as a non-metabolised inducer at a concentration of 0.05 g l^–1 in a continuous culture of P. putida stimulated hydantoinase production up to 80 times the basal level. Using continuous culture conditions established with the model strain, a different strain of P. putida having hydantoinase activity was isolated from commercial mixed cultures of microorganisms. DNA fingerprinting revealed that this new isolate was distinct from strain DSM 84. When used as a probe, the d-hydantoinase gene of strain DSM 84 hybridized with the DNA of the new P. putida isolate.     

Maintenance of two genetic entities by habitat selection

Summary In the laboratory, the two species of copepodsLepeophtheirus thompsoni andLepeophtheirus europaensis, ectoparasites of flatfishes, can meet and mate on at least one host species. In the wild however, these two species are found isolated on their sympatric hosts. Habitat selection theoretically represents a powerful enough mechanism to explain the maintenance of genetic heterogeneity in the wide sense. In this paper, the host colonization process is studied for both parasite species. It is shown that each parasite can develop and reach adult age on each host species. However,L. thompsoni is highly selective; it almost totally refuses to colonize hosts other than its natural one.Lepeophtheirus europaensis, on the contrary, readily infests turbot and brill in single-host experiments, but strongly prefers the brill when it has a choice. It appears that these two genetic entities are sympatrically maintained due to strong habitat selection. Such a pattern could theoretically only occur in a soft-selection context (density dependence). This point is discussed with respect to the different patterns in host use found in the geographical distribution of these parasites.     

The Presence and Role of Transmembrane Transforming Growth Factor-α in Cultures of Rat Liver Epithelial Cells

We assessed the presence and the role of membrane TGF-α in two rat liver epithelial cell lines, either parental or transfected with c-fos proto-oncogene. c-fos overexpressing cells had more TGF-α-like activity in their membranes. When TGF-α was removed by elastase or neutralized, the growth rates of both cell lines were markedly reduced, but to a higher extent for parental cells. If membrane TGF-α seemed to play a key contribution in normal cell growth, both cell lines were unable to react to the addition of soluble TGF-α, showing that these two forms of growth factors are not equivalent.     

X-ray structure of recombinant horse L-chain apoferritin at 2.0 Å resolution: implications for stability and function

The X-ray structure of recombinant horse L-chain (rL) apoferritin, solved at 2.0?Å resolution with a final R factor of 17.9%, gives evidence that the residue at position 93 in the sequence is a proline and not a leucine, as found in earlier sequencing studies. The structure is isomorphous with other apoferritin structures, and we thus draw particular attention to those structural features which can be related to the stability and function of the protein. Analysis of hydrogen bonding and salt bridge interactions shows that dimers and tetramers are the most stable molecular entities within the protein shell: a result confirming earlier biophysical experiments. The stability of horse rL apoferritin to both dissociation into subunits at acidic pH values and to complete unfolding in guanidine chloride solutions is compared with that of other apoferritins. This emphasizes the role played by the salt bridge in the stability of this protein family. The horse rL apoferritin is significantly more resistant to denaturation than horse spleen ferritin, which in turn is more resistant than any human rH apoferritins, even those for which a salt bridge is restored. Finally, this structure determination not only establishes that a preformed pocket exists in L-chain apoferritin, at a site known to be able to bind porphyrin, but also underlines the particular function of a cluster of glutamic acids (E53, E56, E57 and E60) located at the entrance of this porphyrin-binding pocket.     

Transgenic and knockout rodents: Novel insights into mechanisms of body weight regulation

Transgenic animals that over- or underexpress a protein of interest have been used to study obesity development, prevention, and susceptibility to diet-induced obesity such as a high-fat diet. Several transgenic models are resistant to diet-induced obesity including those that overexpress the insulin-sensitive glucose transporter, GLUT4, in adipose tissue only. In this animal there is increased adipose tissue mass but the animal maintains its insulin sensitivity. The overexpression of lipoprotein lipase (LPL) in skeletal muscle and the elimination of a protein kinase A subunit both resulted in lean and obesity resistant animals. By directing the production of the diphtheria toxin A chain to adipose tissue only the resulting animals not only had less adipose tissue mass but were resistant to MSG-induced obesity. Conversely, transgenic models with decreased brown adipose tissue or its function have all resulted in obese animals, highlighting the importance of thermoregulation in body weight maintenance. The use of transgenic technology in the field of obesity has emphasized the regional differences among fat pads as well as the dissimilarity between genders in fuel metabolism. Several transgenic models have separated obesity from insulin resistance allowing the importance of each state to be studied individually. Results using transgenic animals have re-emphasized that obesity is a polygenic disease.     

Marine nematodes of the family Draconematidae (Nemata): a synthesis with phylogenetic relationships

The family Draconematidae is reviewed. Diagnoses of all taxa are updated or emended, basedupon an evaluation of diagnostic features. Aphylogenetic analysis at the genus level based onparsimony suggested that Tenuidraconema belongsto the Draconematinae. A new genus Bathychaetosoma is erected to accomodate B.uchidai (Kito, 1983). It is characterized by acephalic region with a smooth, non-thickened cuticleand numerous cephalic adhesion tubes located posteriorto the head region and extending over more than twohead diameters along the cervical region.     

Modeling of adaptations to physical training by using a recursive least squares algorithm

Busso, Thierry, Christian Denis, Régis Bonnefoy,André Geyssant, and Jean-René Lacour. Modeling ofadaptations to physical training by using a recursive least squaresalgorithm. J. Appl. Physiol. 82(5):1685-1693, 1997.The present study assesses the usefulnessof a systems model with time-varying parameters for describing theresponses of physical performance to training. Data for two subjectswho undertook a 14-wk training on a cycle ergometer were used to testthe proposed model, and the results were compared with a model withtime-invariant parameters. Two 4-wk periods of intensive training wereseparated by a 2-wk period of reduced training and followed by a 4-wkperiod of reduced training. The systems input ascribed to the trainingdoses was made up of interval exercises and computed in arbitraryunits. The systems output was evaluated one to five times per week byusing the endurance time at a constant workload. The time-invariantparameters were fitted from actual performances by using the leastsquares method. The time-varying parameters were fitted by using arecursive least squares algorithm. The coefficients of determinationr² were 0.875 and0.879 for the two subjects using the time-varying model, higher thanthe values of 0.682 and 0.666, respectively, obtained with thetime-invariant model. The variations over time in the model parametersresulting from the expected reduction in the residuals appearedgenerally to account for changes in responses to training. Such a modelwould be useful for investigating the underlying mechanisms ofadaptation and fatigue.

     

Vasomotor instability preceding tilt-induced syncope: does respiration play a role?

Lipsitz, Lewis A., Raymond Morin, Margaret Gagnon, DanKiely, and Aharon Medina. Vasomotor instability precedingtilt-induced syncope: does respiration play a role? J. Appl. Physiol. 83(2): 383-390, 1997.This studyaimed to determine whether alterations in cardiovascular dynamicsbefore syncope are related to changes in spontaneous respiration.Fifty-two healthy subjects underwent continuous heart rate (HR),arterial blood pressure (BP), and respiratory measurements during10-min periods of spontaneous and paced breathing (0.25 Hz) in thesupine and 60° head-up tilt positions. Data were evaluated by powerspectrum and transfer function analyses. During tilt, 27 subjectsdeveloped syncope or presyncope and 25 remained asymptomatic. Subjectswith tilt-induced syncope had significantly greater increases inlow-frequency (0.04-0.15 Hz) systolic BP, diastolic BP, and HRpower during tilt than the asymptomatic subjects(P  0.01). This difference waspresent during spontaneous but not paced breathing. However, averagetidal volume, respiratory rate, minute ventilation, proportion ofbreaths below 0.15 Hz, and low-frequency respiratory power during tilt did not differ between syncopal and nonsyncopal subjects. Transfer magnitudes between low-frequency respiration and BP, and between BP andinterbeat interval, were also similar between groups. Thus vasomotorinstability before syncope is not related to alterations in respirationor the cardiovagal baroreflex but may reflect oscillating centralsympathetic outflow to the vasculature.

     

Glutamine synthetase (GS) expression is reduced in senile dementia of the Alzheimer type

Glutamine synthetase (GS), a metabolic marker of the mature astrocyte, was investigated in the temporal neocortex of postmortem brain samples of 8 cases, either not demented or affected by senile dementia of the Alzheimer type. A negative correlation between the GS protein level and the density of both classical A4 deposits and senile plaques was evidenced. Such a correlation for GS underlies a dysfunction of the astroglial metabolism and particularly of the glutamate and ammonia neutralization. Since GS is sensitive to oxidative lesioning, the changes in GS level that were observed, occurring at the posttranslational stage, might reflect oxidative damage and have severe consequences on the pathological cascade of events.