2-Amino-2-deoxygalacturonic acid in lipopolysaccharides from Pseudomonas aerugimosa.

2-Amino-2-deoxygalacturonic acid was identified as a component of the lipopolysaccharide from Pseudomonas aeruginosa N.C.T.C. 8505. The compound probably occurs in the region of polysaccharide responsible for O-antigenic specificity.     

EFFECT OF REMOVAL OF CO-OCCURRING SPECIES ON DISTRIBUTION AND ABUNDANCE OF ERYTHRONIUM AMERICANUM (LILIACEAE), A SPRING EPHEMERAL

Growth of spring ephemerals in northern forests is limited to early spring when competition for resources from other species is at a minimum. The abundance of resources during this vernal period suggests that spring ephemerals might grow continuously over a wide range of sites, but distributions tend to be patchy. I hypothesized that co-occurring plants that grow later in the season compete for resources to a limited extent, but that competition from these other species is sufficient to restrict the spread of spring ephemerals into unoccupied sites. Population dynamics of Erythronium americanum were compared on sites at the Hubbard Brook Experimental Forest in New Hampshire subjected to varying removals of cooccurring plants. During the 3-year period after removal of only overstory trees the density and frequency of occurrence of Erythronium increased by 225% and 180%, respectively, and removal of all co-occurring vegetation after 1 year's regrowth had an even more pronounced effect (400% and 195% increases, respectively). The abundance of Erythronium in the undisturbed forest did not change over the 3-year period. Elevational distribution of Erythronium also was directly related to the extent of removal of summer plants. Recruitment was mostly vegetative, but flower production on the tree removal site increased by a factor of six, and some distant sites apparently were colonized by seedlings. For several years following large-scale disturbances that eliminate co-occurring vegetation, the vernal growing season is lengthened and resources are more available, and spring ephemerals such as Erythronium americanum exploit these resource-rich opportunities to expand populations and colonize new sites. It appears that, as forest succession proceeds, the size and survival of newly established colonies are gradually constrained by competition from co-occurring species that grow later in the season.     

Bacterial ecology, antibiotics and selection for virulence

The evolution of antibiotic resistance in bacteria is well known. Here I describe possible mechanisms by which an increased rate of re-colonization of vertebrate guts by microbes caused by antibiotic use could lead to selection for increased virulence in currently mutualistic or benign microbes. The importance of understanding both the source and the frequency of colonization in such mutualisms is stressed and the possible importance of pseudo-vertical transmission in the evolution of these systems is discussed. A number of areas requiring experimental investigation are identified.     

Candidate mechanical stimuli for hypertrophy during volume overload.

A myocyte system that senses and responds to mechanical inputs might be activated by any number of features of the time-varying length or force signals experienced by the myocytes. We therefore characterized left ventricular volume and wall stress signals during early volume overload with high spatial and temporal resolution. Left ventricular pressure and volume were measured in open-chest isoflurane-anesthetized male Sprague-Dawley rats 4 and 7 days after surgical creation of an infrarenal arteriovenous fistula or sham operation. Mean wall stresses were calculated by using a simple thick-walled ellipsoidal model. Consistent with previous reports, this surgical model produced a 66% increase in cardiac output and a 10% increase in left ventricular mass by day 7. A number of features of the time-varying volume signal (maximum, mean, amplitude, rates of rise and fall) were significantly altered during early volume overload, whereas many other proposed hypertrophic stimuli, including peak systolic wall stress and diastolic strain, were not. Treating hemodynamic variables more generally as time-varying signals allowed us to identify a wider range of candidate mechanical stimuli for hypertrophy (including some not previously proposed in the literature) than focusing on standard time points in the cardiac cycle. We conclude that features of the time-varying ventricular volume signal and related local deformations may drive hypertrophy during volume overload and propose that those features of the volume signal that also change during pressure overload might be the most interesting candidates for further exploration.     

Characterization of Aspergillus niger catalase

Aspergillus niger catalase has been characterized by a variety of physical techniques including gel filtration, sedimentation rate and equilibrium methods and photon correlation spectroscopy. The catalase has a sedimentation coefficient (S₂₀⁰) of 14.2 ± 0.08 S and diffusion coefficient (D₂₀⁰) of 4.14 ± 0.35 × 10⁻⁷ cm² s⁻¹. The average molecular weight of the catalase from all available data including current sedimentation equilibrium measurements and two previous literature values is 345 000. The frictional ratio of the molecule assuming a hydration parameter similar to that of bovine liver catalase (.3 g H₂O g⁻¹) is 1.103, suggesting that Aspergillus niger catalase has an asymmetric structure with an axial ratio of approximately 3 (the Stokes radius is 5.83 ± 0.49 nm). The titration curve and amino acid analysis indicate that in the native conformation only 23% of the ionizable amino acid residues are titratable between pH 3 and 10.5. Denaturation with sodium n-dodecylsulphate increases the number of titratable groups to 46%. The ratio of anionic to cationic amino acid residues in Aspergillus niger catalase is 2.46 and the isoelectric point is 6.5. The optimum pH for catalytic activity is approximately 7.     

Manganese cycling in an acidic Adirondack lake

There is considerable interest in the chemistry of Mn in acidic waters because of its role in the generation of acid neutralizing capacity during reduction processes, as an adsorbent in element cycling, and as a potential toxicant to aquatic organisms. Temporal and spatial variations in the concentration of Mn were evident in acidic Dart's Lake (1.0–2.3 mol l^–1), located in the Adirondack Region of New York. Seasonal changes in pH and dissolved oxygen concentration had subtle effects on the chemistry and transport of Mn. Despite oversaturation with respect to the solubility of manganite during periods of stratification, vertical deposition of Mn was minimal. The conservative nature of Mn appears to be due to the acidic conditions in Dart's Lake.     

Purification of bovine liver histidyl-tRNA synthetase, the Jo-1 antigen of polymyositis: size of the whole enzyme and its characteristic proteolytic fragments

We have recently reported the marked increase in frequency which can be achieved in the detection of the anti-Jo-1 antibody of polymyositis in serum samples by replacing commercial mixtures of cytoplasmic and nuclear antigens with the purified antigen, histidyl-tRNA synthetase. The present paper describes a method for purifying this antigen and an investigation of its size. Molecular masses previously reported for the enzyme have varied from 85-154 kDa and subunit molecular masses varying from 40-77 kDa have been observed. Several of these fragments are of sizes similar to those of a number of other autoantigens commonly observed in connective tissue diseases. Since the clinical identification of these autoantigens often relies exclusively on size determination by Western blotting, we have characterized the commonly occurring fragments of histidyl-tRNA synthetase lest they confuse such identification. It is concluded that histidyl-tRNA synthetase, like many other aminoacyl-tRNA synthetases, is subject to severe proteolysis during extraction procedures. Several characteristic fragments (Mr = 80, 75, 61, 55, 50 and 45 kDa) result, a finding that provides a satisfactory explanation of the various values previously reported. The intact bovine enzyme is a dimer of molecular mass close to 160 kDa.