Energy-dispersive X-ray analysis of the extracellular cadmium sulfide crystallites of Klebsiella aerogenes

Klebsiella aerogenes forms electron-dense partieles on the cell surface in response to the presence of cadmium ions in the growth medium. These particles ranged from 20 to 200 nm in size, and quantitative energy dispersive X-ray analysis established that they comprise cadmium and sulfur in a 1:1 ratio. This observation leads to the conclusion that the particles are cadmium sulfide crystallites. A combination of atomic absorption spectroscopy, inductively coupled plasma mass spectrometry, and acid-labile sulfide analysis revealed that the total intracellular and bound extracellular cadmium:sulfur ratio is also 1:1, which suggests that the bulk of the cadmium is fixed as extracellular cadmium sulfide. The tolerance of K. acrogenes to cadmium ions and the formation of the cadmium sulfide crystallites were dependent on the buffer composition of the growth medium. The addition of cadmium ions to phosphate-buffered media resulted in cadmium phosphate precipitates that remove the potentially toxic cadmium ions from the growth medium. Electrondense particles formed on the surfaces of bacteria grown under these conditions were a combination of cadmium sulfide and cadmium phosphates. The specific bacterial growth rate in the exponential phase of batch cultures was not affected by up to 2mM cadmium in Tricine-buffered medium, but formation of cadmium sulfide crystallites was maximal during the stationary phase of batch culture. Cadmium tolerance was much lower (10 to 150 M) in growth media buffered with Tris, Bistris propane, Bes, Tes, or Hepes. These results illustrate the importance of considering medium composition when comparing levels of bacterial cadmium tolerance.Abbreviations EDXA Energy dispersive X-ray analysis - AAS Atomic absorption spectroscopy - TEM Transmission electron microscopy - SEM Scanning electron microscopy - ICP-MS Inductively coupled plasma mass spectrometry - ALSA Acid-labile sulfide analysis     

Surgical Treatment of Constipation

A 30-year retrospective review of 544,354 Seattle area hospital admissions yielded 25 patients who underwent surgical therapy for the relief of intractable idiopathic constipation. All patients were refractory to conventional medical treatment consisting of the daily use of laxatives, cathartics, emollients or enemas. Long-term follow-up was available for 13 of the 25 patients. All 13 patients had clinical improvement as a result of the operation. This confirms results reported by other authors. Subtotal colectomy and left hemicolectomy are the procedures generally favored.     

Stimulation of the cyclooxygenase activity of prostaglandin H synthase by salicylate-derived quinhydrones

Two novel salicylate-derived quinhydrones were evaluated for their effect on the kinetics of cyclooxygenase activity of sheep seminal vesicle prostaglandin H synthase. These quinhydrones, which form semiquinone radicals in solution, were designed to resemble oxidized intermediates of salicylic acid metabolism. Although initially investigated for their potential role in irreversible inactivation of cyclooxygenase, these derivatives were found to give three-fold stimulation of this activity. In the absence of arachidonic acid, preincubation of the enzyme with these quinhydrones did not lead to inactivation of the cyclooxygenase activity. These compounds thus resemble the phenolic antioxidants in their effects on the cyclooxygenase activity of the synthase.     

A followup study of the academic attainment and classroom behavior of children with elevated dentine lead levels

To investigate the impact of low-level lead exposure on children's behavior within a natural setting, we assessed the school performance of a sample of 141 elementary school children classified according to dentine lead level. Twenty-two children had “elevated” levels (≥20 parts per million), 71 had “midrange” levels (10.0–19.9 parts per million), and 48 had “low” levels (<10 parts per million). Four types of outcome data were collected: (1) scores on a standardized group intelligence test, (2) teachers' ratings, (3) incidence of academic failure (assignment to remedial aid, grade retention), and (4) observations of classroom behavior. In general, higher dentine lead levels were associated with less favorable school performance, with most covariance-adjustedp-values in the range of 0.05–0.15. The incidence of grade retention was the outcome most strongly related to lead level. The pattern of results suggests a consistent, though weak relationship between children's dentine lead levels and elementary school performance.     

Carbon metabolism and gas exchange in leaves of Zea mays L.

The aim of this work was to investigate the mechanism of formation of triose phosphates and 3-phosphoglycerate during photosynthetic induction in leaves of Zea mays. Simultaneous measurements of gas exchange, chlorophyll a fluorescence and metabolite contents of maize leaves were made. Leaves illuminated in the absence of CO₂ showed a build-up of triose phosphates during the first 2 min of illumination which was comparable to the build-up observed in the presence of CO₂. Isolated mesophyll protoplasts, which lack the Calvin cycle, also showed a build-up of triose phosphates upon illumination. Leaves contained amounts of phosphoglycerate mutase and enolase adequate to account for the formation of triose phosphates and 3-phosphoglycerate from intermediates of the C₄ cycle and their precursors.     

Visual unit,EEG and sustained potential shift responses to biologically significant stimuli in the brain of toads (Bufo bufo)

Summary Visual unit activity, EEG changes and sustained potential shifts (SPS) were recorded from the toad tectum whilst the animal was presented with a visual stimulus. Telencephalic EEGs were also recorded.On the surface of the tectum, retinal unit activity preceded a sustained negative shift in potential and an increase in the amplitude and dominant frequency of the EEG. In deeper layers of the tectum, T5 units with configurational selectivity for wormlike stimuli were found. The activity of these units followed a pronounced SPS and EEG change.Visual unit activity was most pronounced during the negative-going phase of the synchronised EEG, when there was also a small decrease in amplitude of neuronal spikes. Similarities between the latencies and durations of EEGs and SPSs, and their response decrements, on repeated stimulus presentation, implies a close relationship between them not shared by the visual units studied. The specific activity of tectal units is discussed in relation to the correlated EEG and SPS changes, which may form part of an adaptive sensitizing mechanism.Abbreviations EEG electroencephalogram - ERF excitatory receptive field - SPS sustained potential shift - T4, T5 tectal neurons     

Phospholipid vesicle aggregation induced by human myelin basic protein

Human myelin basic protein isolated from the brains of individuals who died with multiple sclerosis was more potent in inducing the aggregation of egg phosphatidylcholine vesicles than was the basic protein isolated from the brains of normal individuals. The portion of myelin basic protein which bound to egg phosphatidylcholine vesicles was separated from the free protein by sucrose density gradient centrifugation. Similar amounts of basic protein from normal or from multiple sclerosis brains are bound to the lipid and no consistent differences in the N^G, N^G dimethyl-arginine content of the protein fractions have been found.     

Selection for Resistance to Leptosphaerulina Leaf Spot in Alfalfa

Significant differences were observed among 11 alfalfa cultivars for the percentage of plants resitant to Leptospbaerulina briosiana after one inoculation. Screening for resistance was done by inoculating 18 day old plants (cv. Europe), held in a moist chamber, with L. briosiana. The self- and cross-progenies of plants resistant to L. briosiana after two inoculations showed slightly higher resistance to Leptosphaerulina leaf spot than the unselected original population but the difference was significant for the cross-progeny only. Larger variations were observed among self-progenies than cross-progenies. No correlation was found between self - and cross-progenies. At least three inoculations may be necessary to eliminate most susceptible plants. Mas selection was as effective as the polycross progeny test to improve the level of resistance of the selected populations as compared with the unselected one but the difference was agronomically unimportant. Under field conditions, the plants selected as resistant after two inoculations in the laboratory showed better resistance to L. briosiana than the susceptible ones but only on the first of three notations. The population derived from plants selected from cv. Europe as resistant to L. briosiana in the laboratory was not significantly more resitant than cv. Europe in the filed but generally showed less foliar infection.     

Synthesis of (±)-16-thioketal and 16-keto prostaglandins

The synthesis of ((±)-16-thioketal and 16-keto PGE₂ methyl ester ( and ) is herein described.