Nutrient and chlorophyll a temporal patterns in eutrophic mountain ponds with contrasting macrophyte coverage

Hydrobiologia - In shallow lakes, macrophytes have important effects on food webs, community structure and nutrient dynamics. For this reason they play a significant role in the restoration of...     

Effect of pH on growth and ethanol production byZymomonas

Summary In a mineral salts medium containing yeast extract, NH₄Cl and glucose (50g/L), the pH range producing the fastest growth ofZ. mobilis was 5.5–6.5 with an apparent optimum at 6.5. At constant growth rate of 0.15hr^–1, the specific rates of glucose utilization (q_s) and ethanol production (q_p) were relatively unaffected by pH over the range 7.0–5.5 but increased sharply as the pH was further decreased below 5.5 to 4.0. Under these conditions the ethanol yield was unaffected by pH over the range 4.0–6.5 but decreased markedly at pH of 7.     

Tyrosine mutations within the alpha platelet-derived growth factor receptor kinase insert domain abrogate receptor-associated phosphatidylinositol-3 kinase activity without affecting mitogenic or chemotactic signal transduction.

A phosphatidylinositol-3 (PI-3) kinase activity of unknown biological function associates with tyrosine kinase-containing proteins, including a number of growth factor receptors after ligand stimulation. In the beta platelet-derived growth factor (beta PDGF) receptor, phosphorylation of a specific tyrosine residue within the kinase insert domain was required for its interaction with this enzyme. We show that substitutions of phenylalanine for tyrosine residue 731 or 742 within the kinase insert domain of the alpha PDGF receptor do not impair PDGF-induced tyrosine phosphorylation of the receptor or of an in vivo substrate, phospholipase C-gamma. Moreover, phosphatidylinositol turnover in response to ligand stimulation is unaffected. However, both lesions markedly impair receptor association with PI-3 kinase. Antiphosphotyrosine antibody-recoverable PI-3 kinase was also dramatically reduced in PDGF-stimulated cells expressing either mutant receptor. Since neither mutation abolished PDGF-induced mitogenesis or chemotaxis, we conclude that alpha PDGF receptor-associated PI-3 kinase activity is not required for either of these major PDGF signalling functions.     

Genetic determinants of glutamine synthetase inDrosophila melanogaster: A gene for glutamine synthetase I resides in the 21B3-6 region

Recombinational and deletion mapping of electrophoretic variants of the glutamine synthetase I isozyme (GSI) in Drosophila melanogaster locates the gene in the 21B region on the second chromosome. We have conducted a genetic analysis of the region extending cytologically from 21A to 21B4-6. Recessive lethal mutations were generated by ethyl methanesulfonate (EMS) and ethyl nitrosourea (ENU) mutagenesis and by hybrid dysgenesis (HD). These lethals fall into seven functional groups, which were partially ordered by complementation with cytologically defined deficiencies of this region generated by hybrid dysgenesis. Two of the EMS- and two of the ENU-induced lethals fulfill biochemical criteria expected for null alleles of the GSI gene.     

Maintenance of Weight Loss: A Needs Assessment

This study identified facilitators and obstacles to maintenance of weight loss following a very-low-calorie-diet and behavior modification program. A survey was mailed to a random sample of 178 program completers and received a 61% response rate; the most frequent follow-up period was more than 2 years. Twenty-nine percent reported weighing the same (within 10 lbs) or less than the end of their participation in the treatment program (maintainers), while 71% reported their present weight was a mean of 65% higher than their initial weight loss (regainers). Maintainers were significantly more likely to report engaging in regular aerobic exercise, attending a maintenance support group, and confidence in their ability to manage their weight in the future, while regainers were more likely to report stress and motivation as frequent weight management obstacles. Respondents consistently identified the need for low/no cost ongoing support. Maintainers and relapsers reported similar challenges in managing their weight, yet with different results, suggesting the need to identify subgroups for which different post-treatment support options could be applied.     

Ionization and binding equilibria of papaverine in ionic micelles studied by 1H NMR and optical absorption spectroscopy

The binding of the vasodilator drug papaverine (PAV) to micelles of zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS), cationic cetyltrimethylammonium chloride (CTAC) and anionic sodium dodecylsulfate (SDS) in aqueous solution was studied by 1H NMR and electronic absorption spectroscopy. In the presence of HPS or CTAC, the apparent pK(a) of PAV decreased by about 2 units, while it increased by about 2 units upon binding to SDS. However, the chemical shift patterns of both protonated (PAVH+) and deprotonated (PAV0) forms of PAV are not sensitive to the type of surfactant. The association constants were estimated as 5 +/- 2 M(-1) for PAVH+-CTAC, 8 +/- 3 M(-1) for PAVH+-HPS, (7 +/- 2) x 10(5) M(-1) for PAVH+-SDS, and 1.5 x 10(3) to 3.0 x 10(3) M(-1) for the complexes of PAV0 with all three types of micelles. Using these data, an electrostatic potential difference on the micelle-water interface was calculated as 150 +/- 10 mV for CTAC, 140 +/- 10 mV for HPS and - 140 +/- 10 mV for SDS. The results suggest that PAV aromatic rings are located in the hydrophobic part of the micelle. The electrostatic attraction or repulsion of the protonated quinoline nitrogen and surfactant headgroups changes the affinity of PAV to micelles and, thus, shifts the ionization equilibrium of PAV. The electrostatic potential of HPS micellar surface is determined by the cationic dimethylammonium headgroup fragment, whereas the anionic sulfate fragment attenuates the effective charge of HPS headgroup.     

Antiproliferative effects of heparin on normal and transformed NIH/3T3 fibroblasts.

We studied the effect of heparin on proliferation and signalling in normal NIH/3T3 fibroblasts, and in cells transformed by different oncogenes. Heparin inhibited the proliferation of normal as well as of v-sis and v-erbB transformed fibroblasts in the presence of serum, but failed to inhibit v-erbB-driven proliferation in serum-starved cultures; under these conditions, heparin inhibited by approximately 50% the proliferation of normal and v-sis- transformed cells. Heparin also inhibited PDGF-induced cell proliferation and inositol lipid turnover in v-sis transformants, but it did not affect PDGF mitogenic signalling in NIH/3T3 fibroblasts.     

Sporulation: an alternative way to recover recombinant proteins from Bacillus subtilis

A recombinant strain of Bacillus subtilis engineered for endocellular expression of human interleukin-1 receptor antagonist (IL-Ira) was subjected to sporulation. The recombinant protein was recovered from the sporulation supernatant in quantities, purity, and activity comparable with those obtained from a traditional cell lysate. Thus, exploitation of this natural mechanism of autolysis could overcome problems of intact protein recovery related to the cell disruption step. (c) 1995 John Wiley & Sons, Inc.