Decrease in insulin-containing secretory granules and mitochondrial gene expression in mouse pancreatic islets maintained in culture following streptozotocin exposure

We have previously described a preferential reduction in the secretory response to nutrient secretagogues in pancreatic mouse islets maintained in culture after in vitro exposure to streptozotocin (SZ). This reduction was associated with an impaired substrate metabolism at the mitochondrial level. To further clarify this issue, mouse pancreatic islets were exposed in vitro to 2.2 mM SZ for 30 min. At 4 h after SZ treatment ultrastructural changes were apparent in the endoplasmic reticulum and Golgi areas of the B-cells. However, 2 and 6 days following SZ exposure the B-cells appeared well preserved, except for a marked decrease in the number of insulin-containing secretory granules. A morphometric analysis of the B-cells 6 days after SZ exposure showed a normal B-cell size and a normal volume fraction of B-cell mitochondria. However, there was a decrease in total islet size and a 13% decrease in the volume fraction of B-cells in the islets. These mouse islets exhibited a decreased content of the mitochondrial DNA-encoded cytochrome b mRNA, as evaluated by dot-blot analysis. As a whole, the data obtained indicate that SZ treatment does not induce a decrease in the number of mitochondria or long-lasting ultrastructural damage to this organelle. However, there is a clear decrease in the cytochrome b mRNA, suggesting that SZ can induce damage to the mitochondrial DNA.     

Purification and properties ofl-serine dehydratase fromLactobacillus fermentum ATCC 14931

l-Serine dehydratase fromLactobacillus fermentum was purified 100-fold. It was stabilized by the presence of 1 mM l-cysteine in 50 mM phosphate buffer. M_r=150,000 was determined by gel filtration. The enzyme consists of four apparently identical subunits (M_r=40,000) that were observed after treatment with sodium dodecyl sulfate. The apparent K_m forl-serine was 65 mM. Fe⁺⁺ was required for the enzymatic activity, and the apparent K_m value for this reaction was 0.55 mM. Maximum enzymatic activity was observed at 45°C and pH 8.0 in 50 mM phosphate buffer. At pH values different from the optimum, a positive cooperativity between substrate molecules was observed. The activation energy of the reaction was 11,400 and 22,800 cal × mol^–1 for temperature values more than and less than 35°C respectively. The purified enzyme showed a maximum absorption between 400 and 420 nm, indicating the presence of pyridoxal-5-phosphate (PLP) as a prosthetic group. The PLP concentration was 0.027 µmoles per milligram of protein. The data suggest that there is 1 mol of PLP for each protein subunit.     

Comparison of methods of repelling mosquitoes

Comparisons were made with human subjects of repellency of free flying Anopheles gambiae using soaps containing deet and permethrin or permethrin alone. The reduction in biting did not differ statistically significantly between these two forms of repellent soap. Some mosquitoes which touched the permethrin soap layer without biting died within the next day. The soap with deet was compared with the same amount of deet in a commercially available stick or as a liquid. Only in the latter form did the repellent show resistance to being washed off by cold water.Electrically heated vaporizing mats containing bio-allethrin were shown to be more effective than smouldering coils containing natural pyrethrins, in that there was more complete prevention of biting, and more rapid knock-down and kill. Operation of the vaporizing mat caused deposition of insecticide on the room surfaces.     

Direct and indirect electron transfer between electrodes and redox proteins

The direct electrochemistry of redox proteins has been achieved at a variety of electrodes, including modified gold, pyrolytic graphite and metal oxides. Careful design of electrode surfaces and electrolyte conditions are required for the attainment of rapid and reversible protein-electrode interaction. The electron transfer reactions of more complex systems, such as redox enzymes, are now being examined. The 'well-behaved' electrochemistry of redox proteins can be usefully exploited by coupling the electrode reaction to enzymes for which the redox proteins act as cofactors. In systems where direct electron transfer is very slow, small electron carriers, or mediators, may be employed to enhance the rate of electron exchange with the electrode. The organometallic compound ferrocene and its derivatives have proved particularly effective in this role. A new generation of electrochemical biosensors employs ferrocene derivatives as mediators.     

Effects of Chromosomal Inversion on Cell Fitness in Escherichia Coli K-12

In an effort to learn what factors might mitigate the establishment of Escherichia coli variants bearing major chromosomal rearrangements, we have examined the effects on cell growth of two inversions between rRNA operons. One of these inversions, IN(rrnD-rrnE), had been propagated in a commonly used subline of E. coli K-12 for approximately 30 yr before its discovery, a fact that illustrates the absence of obvious detrimental effects associated with the inversion. We found that culturing under conditions requiring repeated transition from stationary phase to rapid growth led to the replacement of IN(rrnD-rrnE) cells by cells that had undergone either of two types of additional chromosomal inversion: one type fully restored the wild-type order, while the other partially restored it. The partial reinversion was also between rrn operons, but it left a small transposition. The tendency for overgrowth by these revertants persisted through several rounds of periodic selection. In contrast, the other inversion, IN(rrnG-rrnE), was associated with severe, detrimental effects. The effects of IN(rrnG-rrnE) were also alleviated by full or partial reinversion. The probable relationship between the severity of the effects caused by the inversions and the degree of displacement of the replication origin is discussed. Spontaneous inversion events between rrn operons separated by 18% of the chromosome were estimated to occur at a frequency of roughly 10(-5). If extended to natural situations, the growth disadvantage together with the relatively high frequency of reinversion suggest that clones of cells with an inversion between these rrn operons would be readily overgrown by revertants.     

Factors influencing nitrate depletion in a rural stream

A mass balance procedure was used to analyze rates of nitrate depletion in three adjacent reaches of West Duffin Creek, Ontario, Canada. Daily nitrate losses in individual reaches were highly variable (0.5–24 kg N) during low and moderate stream flows in May–October, 1982–1985. Nitrate removal efficiency (nitrate loss as a % of nitrate input) showed a rapid exponential decline with increased nitrate inputs to each reach. Nitrate losses and nitrate removal efficiency also had a significant negative correlation with stream discharge. The association of large nitrate loads with high stream discharge reduced the nitrate removal capacity of the stream because of shorter residence times and a higher ratio of water volume to stream bed area. Water temperature exhibited a significant positive correlation with nitrate loss which may reflect increased denitrification at higher temperatures.Variations in nitrate losses and nitrate removal efficiency between the three reaches were highly influenced by differences in water residence time. Standarized nitrate losses with respect to water residence time revealed a longitudinal decline in nitrate depletion between the reaches which was associated with a downstream decrease in stream nitrate concentration and in the organic carbon content of fine textured sediments from pool habitats.     

Nitrate depletion in the riparian zone of a small woodland stream

Field enrichments with nitrate in two spring-fed drainage lines within the riparian zone of a small woodland stream near Toronto, Ontario showed an absence of nitrate depletion. Laboratory experiments with riparian substrates overlain with nitrate enriched solutions revealed a loss of only 5–8% of the nitrate during 48 h incubation at 12°C. However, 22–24% of the initial nitrate was depleted between 24 and 48 h when a second set of substrate cores was incubated at 20°C. Short-term (3 h) incubations of fresh substrates amended with acetylene were used to estimate in situ denitrification potentials which varied from 0.05–3.19 g N g^–1 d^–1 for organic and sandy sediments. Denitrification potentials were highly correlated with initial nitrate content of substrate samples implying that low nitrate levels in ground water and riparian substrates may be an important factor in controlling denitrification rates. The efficiency of nitrate removal in spring-fed drainage lines is also limited by short water residence times of < 1 h within the riparian zone. These data suggest that routes of ground water movement and substrate characteristics are important in determining nitrate depletion within stream riparian areas.     

Effect of Naturally Occurring nif Reiterations on Symbiotic Effectiveness in Rhizobium phaseoli

Most naturally occurring strains of Rhizobium phaseoli possess reiteration of the nif genes. Three regions contain nitrogenase structural genes in strain CFN42. Two of these regions (a and b) have copies of nifH, nifD, and nifK, whereas the third region (c) contains only nifH. Strains containing mutations in either nif region a or nif region b had significantly diminished symbiotic effectiveness compared with the wild-type strain on the basis of nodule mass, total nitrogenase activity per plant, nitrogenase specific activity, total nitrogen in the shoot, and percentage of nitrogen. A strain containing mutations in both nif region a and nif region b was totally ineffective. These data indicate that both nif region a and nif region b are needed for full symbiotic effectiveness in R. phaseoli.     

Narrow- and Broad-Host-Range Symbiotic Plasmids of Rhizobium spp. Strains That Nodulate Phaseolus vulgaris

Agrobacterium transconjugants containing symbiotic plasmids from different Rhizobium spp. strains that nodulate Phaseolus vulgaris were obtained. All transconjugants conserved the parental nodulation host range. Symbiotic (Sym) plasmids of Rhizobium strains isolated originally from P. vulgaris nodules, which had a broad nodulation host range, and single-copy nitrogenase genes conferred a Fix⁺ phenotype to the Agrobacterium transconjugants. A Fix⁻ phenotype was obtained with Sym plasmids of strains isolated from P. vulgaris nodules that had a narrow host range and reiterated nif genes, as well as with Sym plasmids of strains isolated from other legumes that presented single nif genes and a broad nodulation host range. This indicates that different types of Sym plasmids can confer the ability to establish an effective symbiosis with P. vulgaris.     

Proposed virulence factors among coagulase-negative staphylococci isolated from two healthy populations

Proposed virulence factors, including multiple antibiotic resistance and slime-mediated adherence, among coagulase-negative staphylococci colonizing healthy individuals from two different study populations were examined. Resistance to methicillin was more commonly seen than initially anticipated. In addition, adherence characteristics, as quantitated by a microtiter plate method, were very similar to those of strains of coagulase-negative staphylococci causing nosocomial infections.