Alteration of the Magnetic Properties of Aquaspirillum magnetotacticum by a Pulse Magnetization Technique

The presence of a narrow shape and size distribution for magnetite crystals within magnetotactic organisms suggests strongly that there are species-specific mechanisms that control the process of biomineralization. In order to explore the extent of this control, cultures of Aquaspirillum magnetotacticum in the exponential growth phase were exposed to increasing magnetic pulses with the aim of separating cell populations on the basis of their magnetic coercivities. Isothermal remanent magnetization and anhysteretic remanent magnetization studies were performed with freeze-dried magnetic cells after the remagnetization treatment. Subpopulations of A. magnetotacticum that showed an increase in coercivity correlated with the intensity of the magnetic pulses were isolated. After successive subcultures of the remaining north-seeking cells, a maximum bulk coercivity (H_b^max) of 40 mT was obtained after treatment with a 55-mT pulse. Although we obtained A. magnetotacticum variants displaying higher coercivities than the wild-type strain, changes in crystal size or shape of the magnetite crystals were below reliable detection limits with transmission electron microscopy. Attempts to shift the coercivity towards higher values caused it to decrease, a change which was accompanied by an increase in magnetostatic interactions of the magnetosome chains as well as an increase in the cell population displaying an abnormal distribution of the magnetosome chains. Ultrastructural analyses of cells and magnetosomes revealed the appearance of cystlike bodies which occasionally contained magnetosomes. The increase in cystlike cells and abnormal magnetosome chains when higher magnetic pulses were used suggested that magnetosomes were collapsing because of stronger interparticle magnetostatic forces.     

Phosphofructokinase from mollusc muscle is activated by phosphorylation.

Phosphofructokinase was purified from muscle tissue of two different molluscs, edible snails, Helix pomatia (gastropoda), and mussels, Mytilus edulis (bivalvia). Under denaturing conditions, both enzymes had a molecular mass of 82 kDa. In the presence of ATP-Mg2+, the enzymes were rapidly phosphorylated in vitro by the catalytic subunit of cyclic AMP (cAMP)-dependent protein kinase purified from snail muscle and also by the C subunit of protein kinase from bovine heart. The extent of phosphorylation was 0.6 and 0.5 phosphate residues per subunit for the snail and the mussel phosphofructokinase, respectively. Phosphorylation of both phosphofructokinases effected a decrease in ATP inhibition at neutral or slightly acidic pH values and increased the affinity for fructose 6-phosphate. The resulting activation in the presence of suboptimum fructose 6-phosphate concentrations was more distinct for the snail enzyme. In addition, phosphorylated phosphofructokinase from mussels exhibited a marked increase in Vmax when activated by either 5'-AMP or fructose 2,6-bisphosphate.     

Life cycle ofPseudodiamesa branickii (Chironomidae) in a small upland stream

The generation time ofP. branickii was studied using larval samples in conjunction with rearing experiments and continuous collection of egg masses across one year. This species produced three generations per year in a central German stream (280 m a.s.l., 50° 40 N). Its generation time was variable and obviously influenced by the photoperiod to which eggs and larvulae were subjected. It is thus concluded that two strains ofP. branickii were present in a single population, one bivoltine and the other trivoltine.     

Effect of glucocorticoids on alkaline phosphatase, alanine aminotransferase, and gamma-glutamyltransferase in cultured dog hepatocytes

Glucocorticoid(GC)-induced hepatopathy in the dog is characterized by abnormal liver morphology and increases in serum alanine aminotransferase (ALT), gamma-glutamyltransferase (GGT), and the liver alkaline phosphatase isoenzyme (LALP) and by the appearance of an unusual isoenzyme of alkaline phosphatase known as the corticosteroid-induced alkaline phosphatase isoenzyme (CALP). It has not been shown whether the increases in serum ALT, GGT, and LALP are as a result of an increase in production of these enzymes or as a result of the GC-induced hepatocellular swelling and possible membrane alterations. Also, it has been assumed that the mechanism of production of CALP is via GC-induced gene derepression and de novo protein synthesis; however, this hypothesis has not been directly tested. Using isolated dog hepatocytes maintained in a confluent monolayer culture in the presence and absence of GC or cyclic AMP, no statistical increase in serum ALT, GGT, or LALP was observed. A combination of GC and cyclic AMP also caused no statistical increase in ALT and GGT; however, we demonstrate that these conditions clearly stimulated the de novo synthesis of LALP. These conditions do not induce the synthesis of CALP as determined by a sensitive immunoassay. The data obtained using this in vitro model suggest that the primary mechanism(s) of the in vivo increase of serum ALT and GGT in GC treated dogs may be other than that of de novo protein synthesis. Likewise, in vitro production of CALP may be a mechanism more complex than the conditions tested in this study.     

Isolation and structure elucidation of a novel 5-kDa peptide from neurohaemal lobes of the corpora cardiaca of Locusta migratoria (Insecta, Orthoptera)

Two predominant peptides have been isolated from neurohaemal lobes of corpora cardiaca of 8000 adults of Locusta migratoria. Both peptides have been unambiguously characterized by automated peptide microsequencing and liquid secondary-ion mass spectrometry as a 50-residue peptide (5K peptide) and a 48-residue isologue (5K' peptide). Computer search of sequence data banks did not reveal any significant similarity with other identified proteins. The 5K peptides are remarkably rich in alanine residues (25%) and contain a stretch of five consecutive alanines. This structure suggests that these molecules could correspond to spacer peptides. This assumption is corroborated in the accompanying paper [Lagueux et al. (1990) Eur. J. Biochem. 187, 249-254] on the molecular cloning of the precursor protein which attributes to the 5K peptides a role analogous to that of the C peptides of insulins.     

Mechanism of degradation of duplex DNA by the DNase induced by herpes simplex virus

Reaction intermediates formed during the degradation of linear PM2, T5, and λ DNA by herpes simplex virus (HSV) DNase have been examined by agarose gel electrophoresis. Digestion of T5 DNA by HSV type 2 (HSV-2) DNase in the presence of Mn²⁺ (endonuclease only) gave rise to 6 major and 12 minor fragments. Some of the fragments produced correspond to those observed after cleavage of T5 DNA by the single-strand-specific S1 nuclease, indicating that the HSV DNase rapidly cleaves opposite a nick or gap in a duplex DNA molecule. In contrast, HSV DNase did not produce distinct fragments upon digestion of linear PM2 or λ DNA, which do not contain nicks. In the presence of Mg²⁺, when both endonuclease and exonuclease activities of the HSV DNase occur, most of the same distinct fragments from digestion of T5 DNA were observed. However, these fragments were then further degraded preferentially from the ends, presumably by the action of the exonuclease activity. Unit-length λ DNA, EcoRI restriction fragments of λ DNA, and linear PM2 DNA were also degraded from the ends by HSV DNase in the same manner. Previous studies have suggested that the HSV exonuclease degrades in the 3′ → 5′ direction. If this is correct, and since only 5′-monophosphate nucleosides are produced, then HSV DNase should “activate” DNA for DNA polymerase. However, unlike pancreatic DNase I, neither HSV-1 nor HSV-2 DNase, in the presence of Mg²⁺ or Mn²⁺, activated calf thymus DNA for HSV DNA polymerase. This suggests that HSV DNase degrades both strands of a linear double-stranded DNA molecule from the same end at about the same rate. That is, HSV DNase is apparently capable of degrading DNA strands in the 3′ → 5′ direction as well as in the 5′ → 3′ direction, yielding progressively smaller double-stranded molecules with flush ends. Except with minor differences, HSV-1 and HSV-2 DNases act in a similar manner.     

Effect of human leukocyte interferon on human lymphocytes in vitro: cytogenetic studies

Mitogen-stimulated lymphocytes from 8 healthy donors were exposed to interferon, and cytogenetic studies were preformed. The response of lymphocytes to the mitogens phytohemagglutinin (PHA), concanavalin A (con A) and pokeweed mitogen (PWM) was inhibited by interferon, whereas an increased number of structural chromosomal aberrations was not detected. Further investigations of the cytogenetic effects of interferon are needed.     

Ethylene formation by germinating,Drechslera graminea — Infected barley (Hordeum sativum) grains: A simple test for fungicides

Grains of barley (Hordeum sativum L.); infected with the parasitic, systemic fungus Drechslera graminea, produce more ethylen than uninfected controls. Treatment of infected grains with mercury-free fungicides yields a differentiated suppression of the ethylene evolution 7 d after the beginning of germination. Suppression of visible symptoms (chlorotic stripes on leaves) appearing six to eight weeks after germination of infected, untreated seeds correlates with the decrease in ethylene formation after treatment with fungicides. The gaschromatographic ethylene determination thus allows for an early and reliable (significance higher than 99.9%) differentiation of fungicidal activities against the barley stripe disease.Abbreviations ACC I-aminocyclopropane-1-carbonic acid - CD critical difference     

Selfcompatibility in microspore-derived doubled-haploid rye lines and single grain selection for alkylresorcinol content

Summary From a total of 138 green androgenetic rye lines, 25 were fertilized and examined in field tests: 7 were heterozygous and 18 were homozygous. Of the homozygotes, 4 turned out to be selfincompatible, while 14 set seed after selfing. Four characters were analyzed in detail: 100 kernel weight, plant height, ear length, and alkylresorcinol content. Here we present the first approach in prescreening selfcompatible androgenetic doubled-haploid rye plants with the single grain procedure. The usefulness of this method was confirmed by quantitative resorcinol determination in the following generation. Furthermore, it was demonstrated that all the homologues of the alkylresorcinol were equally reduced. For all characters the means of the different anther derived lines exceeded the means of the controls in both directions, to the positive as well as to the negative side. The incorporation of such a haploid breeding step into breeding programs is discussed.Dedicated to Professor Dr. G. Melchers, on the occasion of his 75th birthday, who initiated this work by forming the project-groups Haploide in der Pflanzenzüchtung