Effectiveness of phytoplankton control by large-bodied and small-bodied zooplankton

Employingin situ enclosures containing inocula of the lake zooplankton (mainlyDaphnia galeata, Daphnia cucullata andBosmina spp.) from a moderately eutrophic Lake Ros (Northern Poland) or large-bodiedDaphina magna, the following observations on succession of phytoplankton were made: 1) whereasD. magna could control the density of all the photoplankton size classes, the lake zooplankton could not suppress the large-sized phytoplankters or net phytoplankton; 2) the lake zooplankton was able to control the density of small algae (< 50μm), but its effect on large algae may be opposite: a promotion of net phytoplankton growth by removing small-sized algae which can out-compete net phytoplankton for limited PO₄-P resources (<5μg P l⁻¹). Since efficiency of phytoplankton density control byD. magna decreased with an increase in net phytoplankton abundance, biomanipulation could not be successful without introducing or maintaining a high population of large-bodied cladoceran species before high densities of large algae would make the control of phytoplankton inefficient.     

Glucagon and epinephrine-stimulated phospholipid methylation in hepatic microsomes

Phospholipid methylation by hepatic microsomes was measured following glucagon or epinephrine administration either to intact rats or to the isolated perfused liver. Both hormones stimulated the methylation measured as the incorporation of S-adenosyl-L-[methyl-³H]methionine into phospholipids. The labeled products were identified by thin layer chromatography and most of the counts were found to be incorporated into phosphatidylcholine. The stimulatory effects of the hormones were evident already 5 minutes following hormone administration both in $\text{in vivo}$ and in $\text{in vitro}$. The observed stimulation of the methylation process by glucagon and epinephrine might be related to the previously reported stimulatory effect of these hormones on the microsomal Ca²⁺-ATPase, and indicate that methylation process(es) might mediate some of the effects of these hormones.     

Mutations within an intron and its flanking sites: Patterns of novel polypeptides generated by mutants in one segment of the cob-box region of yeast mitochondrial DNA

Summary We have undertaken a systematic examination of the polypeptides accumulating in thirteen (out of 23) mutants in the intron cluster box7 and its flanking clusters box2 and box9 of the cob-box (cytochrome b) region of the mitochondrial genome of Saccharomyces cerevisiae. We have subjected these polypeptides to fingerprint analysis, both sequential and in parallel, with two proteases in order to disclose sequence homologies and differences between the different novel polypeptides themselves, and between them and the wild type product of the gene, i.e. apocytochrome b. One of our aims has been to establish the existence of possible correlations between the nature of the novel polypeptides and the fine structure genetic map of that segment of the mitochondrial genome.Our results show that all box7 mutants accumulate the following set of polypeptides not seen in wild type cells: a) a characteristic set of large polypeptides consisting of three species: p56, p42 and p35 or p34.5; b) a polypeptide p23; c) a much shorter fragment (of which the apparent molecular weight varies from 12.5 to 13, according to the mutation) with the exception of two mutants; d) in addition, the majority accumulate in varying amounts a polypeptide p30 closely related to but not identical with apocytochrome b.Moreover only two box7 mutants accumulate a polypeptide in the range of mobilities corresponding to 25–27 Kd (referred to as class p26) while such a polypeptide is seen in all box9 and box2 mutants examined with one exception in box2.Only one mutant in box2 resembles box7 mutants with respect to criterion a), and no box2 or box9 mutants resemble box7 mutants with respect to criterion c); criteria b) and d) appear to apply equally well to mutants in all three clusters.Fingerprint analysis, carried out with polypeptides p56, p42, p35, p34.5, p30, p26, p23, discloses that a) The polypeptides belonging to the same class of mobility exhibit very similar if not identical sequences in various cases. b) These polypeptide classes, except p56, p42 and p26, share considerable sequence homologies with wild type apocytochrome b, perhaps encompassing 50% or more of the wild type sequences. b) Polypeptides belonging to the classes p42 and p26 exhibit less extensive but nevertheless significant homologies with the wild type sequence. c) Sequences in polypeptides belonging to class p56 are virtually indistinguishable from ones in cytochrome oxidase subunit I.The inferences from these findings are 1) one gene can produce a multiplicity of polypeptide products that share a common sequence at the promoter-proximal (N-terminal) portion, but diverge beyond these regions of homology. 2) Both the multiplicity of products in single mutants, and the protein structure found, argue against the divergent segments to be due to frameshift terminations, and instead suggest that the novel products are consequences of mRNA processing defects (excision and/or ligation) at and near intron regions. 3) Mutations at edges and the center of an intron can generate similar polypeptide patterns, i.e. produce analoguous mRNA processing defects. 4) Mutations in exons, at their boundary with introns, can produce polypeptide patterns indistinguishable from those at the neighbouring intron; they diverge and eventually become typically exonlike in mutants localized at increasing distances from the boundary. 5) Taken together these findings argue that pre-mRNA processing extends beyond the boundaries of the intron proper and that certain exonsequences participate in excision and ligation. 6) Accumulated pre-mRNAs, resulting from defects in splicing can be translated. 7) Product p56 is formally analogous to p23, as a faulty but highly conserved partial product of the wild type protein, the former of Cox I (oxi3 gene), the latter of the cob-box gene proper. Therefore both genes may utilize identical RNA processing elements which are affected by box7 mutations. 8) A small amount of product similar to p56 may accumulate even in some wild types but not in others. This observations suggests that in certain nuclear backgrounds RNA processing may be more error-prone than in others.Publication No. XXXX from the Department of Chemistry, Indiana UniversitySupported by Research Grant GM 12228 from the National Institute of General Medical Sciences, National Institutes of Health; recipient of Research Career Award K06 05060 from the same Institute.Supported by Délégation Générale à la Recherche Scientifique et Technique grant n⁰ 78-70341     

Transport of Ammonium and Methylammonium Ions by Azotobacter vinelandii

Ammonium and methylammonium are rapidly taken up by cultures of Azotobacter vinelandii respiring in the presence of succinate. The rate of methylamine uptake increased with external pH from 5.5 to 7.5 but increasing the pH further to 8.5 had little effect on activity, indicating that methylammonium cation rather than uncharged methylamine is the permeant species. The kinetics of methylammonium entry followed the Michaelis-Menten relationship, yielding a K_m of 25 μM and a V_max of 3.8 nmol/min per mg of cell protein. At saturating concentrations ammonium was taken up at rates 30-fold higher than those for methylammonium. Ammonium was a competitive inhibitor of methylammonium uptake and gave an inhibition constant of 1 μM. Ammonium derivatives were inhibitors of methylammonium entry in order of effectiveness: hydrazine > methylhydrazine > formamidine > guanidine > dimethylamine > ethylamine; amides and amino acids did not block uptake. Likewise, metal cations inhibited in the order Tl⁺ > Cs⁺ > Rb⁺, whereas Na⁺, K⁺, and Li⁺ produced no significant effect. Methylammonium uptake was blocked in cells exposed to an uncoupler, p-trifluorome-thoxycarbonyl cyanide-phenyl hydrazone or gramicidin D, but not with dicyclo-hexylcarbodiimide or arsenate. Valinomycin stimulated methylammonium entry into cells in a K⁺-free medium but prevented entry in the presence of 10 mM K⁺. Monensin and nigericin had little effect on transport. These results indicate that methylammonium and ammonium ions enter A. vinelandii electrogenically via a specific transporter.     

Purification and Properties of Deoxyribonucleic Acid Binding Factor Isolated from the Surface of Streptococcus sanguis Cells

Deoxyribonucleic acid (DNA) binding factor (BF) was found in surface fluids from competent and noncompetent cells of Streptococcus sanguis strains Challis, Wicky, and Blackburn. Fluids from noncompetent cells exhibited about 10% BF activity compared with extracts from competent cells. BF from competent Wicky cells was purified to homogeneity by electrophoresis and immunodiffusion. Purified BF preparations exhibited slight endonucleolytic activity, directed mainly against single-stranded DNA. Nucleolytic and DNA binding activities present in purified BF could be separated by polyacrylamide gel electrophoresis. Purified BF was sensitive to proteolytic enzymes and to phospholipase D, and its activity was stimulated in the presence of low Triton X-100 concentrations. The protein component of BF is a single, monomeric polypeptide with a molecular weight of 56,000 and an isoelectric point of pH 5.8. Binding of purified BF to DNA was a very rapid process at the optimum temperature, pH, and ionic strength and led to the formation of fast-sedimenting complexes. Purified BF was tested for several properties. It exhibited higher affinity to single- than to double-stranded DNA. It bound poorly to glucosylated phage T4 and single-stranded, synthetic polydeoxyribonucleotides and did not bind to RNA. It protected single-stranded DNA against nuclease S₁ action but did not protect native DNA against deoxyribonuclease I action. No evidence was found for unwinding activity, using double-stranded DNA as a substrate.     

Solubilization of microsomal phosphoethanolaminetransferase by octyl glucoside

Phosphoethanolaminetransferase of high specific activity was solubilized from rat liver microsomes with the non-ionic detergent octyl glucoside. The solubilization method is fast and simple, allowing for processing of large amounts of material. The solubilized enzyme is stable. It contains virtually no phosphocholinetransferase activity. A preliminary characterization of the enzyme, with both diacyl- and alkylacyl-glycerol as substrate, is given. For the reaction, the lipid substrates were incorporated into artificial phospholipid bilayers (liposomes).     

Periodic Forces Trigger a Complex Mechanical Response in Ubiquitin

Mechanical forces govern physiological processes in all living organisms. Many cellular forces, for example, those generated in cyclic conformational changes of biological machines, have repetitive components. In apparent contrast, little is known about how dynamic protein structures respond to periodic mechanical information. Ubiquitin is a small protein found in all eukaryotes. We developed molecular dynamics simulations to unfold single and multimeric ubiquitins with periodic forces. By using a coarse-grained representation, we were able to model forces with periods about 2 orders of magnitude longer than the protein's relaxation time. We found that even a moderate periodic force weakened the protein and shifted its unfolding pathways in a frequency- and amplitude-dependent manner. A complex dynamic response with secondary structure refolding and an increasing importance of local interactions was revealed. Importantly, repetitive forces with broadly distributed frequencies elicited very similar molecular responses compared to fixed-frequency forces. When testing the influence of pulling geometry on ubiquitin's mechanical stability, it was found that the linkage involved in the mechanical degradation of cellular proteins renders the protein remarkably insensitive to periodic forces. We also devised a complementary kinetic energy landscape model that traces these observations and explains periodic-force, single-molecule measurements. In turn, this analytical model is capable of predicting dynamic protein responses. These results provide new insights into ubiquitin mechanics and a potential mechanical role during protein degradation, as well as first frameworks for dynamic protein stability and the modeling of repetitive mechanical processes.     

Preparation of an enantiomerically pure, highly porous metalloorganic crystal

We report the synthesis and the structure determination of tris-(4,5-diazo-spiro-bifluorene)ruthenium(II) chloride, a chiral building block whose racemic mixture solution spontaneously resolves and forms two crystalline, enantiomerically pure, porous networks composed exclusively of the Λ or Δ atropisomers. The extended chiral channels are occupied by water molecules (approximately 20% by weight) and the chloride counter-ions.     

Impact of the alien plant Impatiens glandulifera on species diversity of invaded vegetation in the northern foothills of the Tatra Mountains,Central Europe

Plant Ecology - The impact of exotic annual Impatiens glandulifera on invaded European vegetation is ambiguous; there are studies reporting considerable negative as well as weak or even no impact...