Three new Ecuadorian species of Axinaea (Melastomataceae)

Three new Ecuadorian species of Axinaea (Melastomataceae) are described: Axinaea flava, A. glauca, and A.lawessonii. All three species are endemic to southern Ecuador. Axinaea flava and A.glauca grow in the transition zone between montane forest and pbramo. They share characters such as shrubby habit, dense to moderate pubescence and coriaceous, rigid, erect leaves, which may be related to their high altitude habitat. Axinaea flava is the only species of the genus with a yellow corolla. Axinaea glauca, a shrub less than 1 m high, is the smallest Axinaea species known. Field observations show that these two species have a restricted habitat and their known populations are small, probably less than 100 individuals. The third species, A.lawessonii, grows in wet montane forests. It can grow as a shrub or a slender tree and its leaves are glabrous and less rigid than those of A.flava and A.glauca, characters which are probably a consequence of the more humid and benign habitat. Axinaea lawessonii is the only species of the genus in which the leaf margins have uncinate teeth. The species is rather frequent in southern Ecuador and has been collected in a dozen localities, most of which are within the Podocarpus National Park.     

Optimized BlaM-transposon shuttle mutagenesis of Helicobacter pylori allows the identification of novel genetic loci involved in bacterial virulence

Helicobacter pylori is an important etiologic agent of gastroduodenal disease in humans. In this report, we describe a general genetic approach for the identification of genes encoding exported proteins in H. pylori. The novel TnMax9 mini-blaM transposon was used for insertion mutagenesis of a H. pylori gene library established in Escherichia coli. A total of 192 E. coli clones expressing active β-lactamase fusion proteins (BlaM⁺) were obtained, indicating that the corresponding target plasmids carry H. pylori genes encoding putative extracytoplasmic proteins. Natural transformation of H. pylori P1 or P12 using the 192 mutant plasmids resulted in 135 distinct H. pylori mutant strains (70%). Screening of the H. pylori collection of mutant strains allowed the identification of mutant strains impaired in motility, in natural transformation competence and in adherence to gastric epithelial cell lines. Motility mutants could be grouped into distinct classes: (i) mutant strains lacking the major flagellin subunit FlaA and intact flagella (class I); (ii) mutant strains with apparently normal flagella, but reduced motility (class II), and (iii) mutant strains with obviously normal flagella, but completely abolished motility (class III). Two independent mutations that exhibited defects in natural competence for genetic transformation mapped to different genetic loci. In addition, two independent mutant strains were isolated by their failure to bind to the human gastric carcinoma cell line Katoill. Both mutant strains carried a transposon in the same gene, 0.8 kb apart, and showed decreased autoagglutination when compared to the wild-type strain.     

General relation between variance-time curve and power spectral density for point processes exhibiting 1/f β-fluctuations,with special reference to heart rate variability

Counting statistics in the form of the variance-time curve provides an alternative to spectral analysis for point processes exhibiting 1/f ^β-fluctuations, such as the heart beat. However, this is true only for β<1. Here, the case of general β is considered. To that end, the mathematical relation between the variance-time curve and power spectral density in the presence of 1/f ^β-noise is worked out in detail. A modified version of the variance-time curve is presented, which allows us to deal also with the case β?1. Some applications to the analysis of heart rate variability are given.     

Selective synthesis of depsipeptides by the immobilized multienzyme enniatin synthetase

Summary The multifunctional enzyme enniatin synthetase was immobilized by adsorption to propyl agarose. The immobilized multienzyme retained 45% of the activity of the free enzyme; an operational half-life of about 15 h was estimated. Selective synthesis of several different enniatin homologues was achieved with propyl agarose-bound enniatin synthetase. In addition to enniatin A, B, and C formation, a selective synthesis of non-naturally occurring depsipeptides, containing norvaline, norleucine, or -aminobutyric acid as sole amino acid moieties, was observed.     

The pericellular boundary layer modulates acetylcholine receptor stability in cultured myotubes

Degradation of acetylcholine receptors in cultured chicken myotubes was measured by release into the medium of radioactivity from 125I-labeled alpha-bungarotoxin. Disturbance of the pericellular boundary layer by stirring of the culture medium shortened the half-life of receptor in the membrane from 24 to 12 h. The effect could not be explained by dissociation of toxin-receptor complexes or by conditioning of the bulk phase of the medium. The rates of synthesis and degradation of total cell protein and the degradation of lactoperoxidase-iodinated surface protein were not affected by medium stirring. The loss of glucosamine-labeled material from the cells was enhanced by stirring, however, and this resulted entirely from the increased shedding of high molecular weight glycosubstances from the cells. Cells in stirred cultures contained lower levels of surface coat material stainable with colloidal thorium. These results indicate that glycosubstances of the pericellular matrix protect ACh receptors from degradation.     

Analysis of the HLA-ABC linkage disequilibrium: Decreasing strength of gametic association with increasing map distance

Summary 1242 HLA-ABC haplotypes of the North German population (Hamburg) as deduced by family analyses are described. They are in perfect agreement with recently published data by Mayr (1977) from Austria (Vienna) in all parameters tested: frequency of the single HLA-alleles, haplotype distribution and linkage disequilibrium values. Gametic association studies revealed that 69.4% of the B and C genes (map distance 0.2 cM) 36.9% of the A and C genes (0.6 cM), but only 23.2% of the A and B genes (0.8 cM) were significantly more often combined than expected due to their frequencies. From these findings it seems likely that the linkage disequilibrium within the MHC is rather due to a short evolutionary period than to selective forces. Some observations as to the most common European haplotype A1,B8 are discussed.     

Age-dependent content of polymerized lipids in Sphagnum fuscum

The polymerized lipids of Sphagnum fuscum cell wall fragments were found to be composed of long chain hydroxy acids, long chain dicarboxylic acids, fatty alcohols and fatty acids. Their content, on a dry weight basis, was low in the topmost 3 cm of the shoot and increased with shoot age (and depth). A pronounced increase (16-fold) occurred in the contents of hydroxy acids which comprised 76% of the totals at the depth of 40–43 cm. The increase at the depth of 40-43 cm is considered to be at least partly associated with the frequently found destruction of the most suscptible part, the thin-walled stem center. The results suggest that aliphatic lipid polymers are present and acumulated in cell walls resistant to breakdown.