Serological comparisons of seed proteins of some representatives of the genusAllium

Results obtained by comparison of similarity of seed protein spectra of 15 species of the genusAllium (in 22 samples) by means of immunochemical methods more or less correspond to the contemporary division of this genus. Species belonging to the sectionCepa (according to Vvedenskiy) andPhyllodolon have very similar spectra, which suggests that they either should be allocated to one sectionCepa or to two subsections (Cepa andPhyllodolon). Species belonging to the subgenusRhizirideum considerably differ in seed proteins. The investigated species of the subgenusMelanocrommyum show the most distinct spectrum of all the other analyzed representatives, less marked differences were found in the case of the representatives of the subgenusAllium.     

Influence of Manganese on Growth of a Sheathless Strain of Leptothrix discophora

Mn²⁺ exerted various effects on the growth of Leptothrix discophora strain SS-1 in batch cultures depending on the concentration added to the medium. Concentrations of 0.55 to 5.5 μM Mn²⁺, comparable to those in the environment from which strain SS-1 was isolated, decreased cell yield and prolonged stationary-phase survival, but did not affect growth rate. Elevated concentrations of 55 to 910 μM Mn²⁺ also decreased cell yield and prolonged survival, but growth rate was decreased as well. The addition of 1,820 μM Mn²⁺ caused a decline in cell numbers followed by an exponential rise after 80 h of incubation, indicating the development of a population of cells resistant to Mn²⁺ toxicity. When 360 μM Mn²⁺ or less was added to growth flasks, Mn²⁺ was oxidized to manganese oxide (MnO_x, where x is ~2), which appeared as brown particles in the medium. Quantification of Mn oxidation during growth of cultures to which 55 μM Mn²⁺ was added showed that nearly all of the Mn²⁺ was oxidized by the beginning of the stationary phase of growth (15 to 25 h). This result suggested that the decrease in cell yield observed at low and moderate concentrations of Mn²⁺ was related to the formation of MnO_x, which may have bound cationic nutrients essential to the growth of SS-1. The addition of excess Fe³⁺ to cultures containing 55 μM Mn²⁺ increased cell yield to levels near those found in cultures with no added Mn²⁺, indicating that iron deprivation by MnO_x was at least partly responsible for the decreased cell yield.     

Role of calcium in the initiation of fast axonal transport of protein: Effects of divalent cations

Fast axonal transport of [³H]protein has been examined in bullfrog primary afferent neurons incubated in media supplemented with divalent cations that can act as agonists or antagonists of calcium ions. Incubation in calcium-free medium (CFM) had no effect on the rate of transport, but reduced the amount of transported [³H]protein by 40–60% relative to transport in the contralateral preparation maintained in normal medium. Preparations incubated in CFM supplemented with 1.8 mM SrCl₂ (equimolar to the CaCl₂ concentration in normal medium) carried out transport at control levels. Incubation conditions in which primary afferent somata were exposed to the Sr²⁺-medium while nerve trunks were maintained in CFM also supported normal transport. By contrast, selective exposure of nerve trunks to Sr²⁺-medium, and somata to CFM resulted in a reduced level of transport similar to that observed when the whole preparation was incubated in CFM. The depression of transport resulting from incubation in CFM was shown to be reversible when preparations were transferred from CFM to either Sr²⁺-supplemented CFM or to normal medium. By contrast to the effects of Sr²⁺, Ba²⁺ (up to 18 mM) did not substitute for Ca²⁺ in the transport process. When normal medium was supplemented with calciumantagonist cations, the amount of transport was depressed (Co²⁺ > Mn²⁺ >> Mg²⁺), with no concomitant effect on the rate of transport. Results of studies with Co²⁺, as well as those with Sr²⁺, suggest that a major locus of action of these cations is within the neuronal soma at a step subsequent to protein synthesis, and prior to the onset of protein translocation via the transport system. Thus, it is inferred that these divalent cations affect a calcium-dependent step that occurs during the initiation phase of fast axonal transport.     

Characterization of adaptability components of Brazilian isolates of Macrophomina pseudophaseolina

Macrophomina pseudophaseolina is a new Macrophomina species reported on different crop and weed species in Brazil, India and Senegal, but to date there are no studies about its adaptability components. In this work, a collection of 62 M. pseudophaseolina isolates obtained from roots of the weed species Trianthema portulacastrum and Boerhavia diffusa collected in Northeastern Brazil, was used to: (a) study the effect of temperature and salinity on mycelial growth, (b) to determine their sensitivity to the fungicide carbendazim and (c) to assess their aggressiveness on melon and watermelon seedlings. Results showed variability among M. pseudophaseolina isolates. The optimum temperature for mycelial growth ranged between 26.4 and 38.1ºC. NaCl reduced the in vitro growth of all isolates, which were also highly sensitive to the fungicide carbendazim, exhibiting EC₅₀ values ranging from 0.013 to 0.089 mg/L a.i. Disease severity values on melon and watermelon seedlings showed that M. pseudophaseolina isolates were more aggressive in melon than in watermelon. Information about adaptability components of M. pseudophaseolina obtained in this study could be incorporated on breeding programs for melon and watermelon crops.     

Influence of Volume of Nutrient Agar Medium on Development of Colonies of Marine Bacteria

Zusammenfassung Bei der Bestimmung der Anzahl Bakterien in frisch genommenen Seewasserproben mit dem Plattengußverfahren reduziert eine Agarmenge von über 10 ml die Anzahl sich entwickelnder Kolonien. Die erhaltenen Zahlen sind im allgemeinen am höchsten und die Ergebnisse am besten reproduzierbar, wenn genau 10 ml des Nähragars benutzt wird im Gegensatz zu unbestimmten Mengen zwischen 5 und 30 ml. Obgleich auch andere Faktoren eine Rolle spielen, wird der ungünstige Einfluß von Agarmengen, die merklich größer als 10 ml sind, in erster Linie den langsameren Abkühlungsraten während des üblichen Plattengußverfahrens zugeschrieben. Wenn Nähragar von 42° C bei Raumtemperatur (22–24° C) in Pyrex-Petrischalen gegossen wurde, kühlten 10 ml in ca. 1 min. auf 30° C ab, während 5 bis 24 min. gebraucht wurden, um Agarmengen von 20 bis 50 ml von 42° C auf 30° C abzukühlen. Viele marine Bakterien werden geschädigt, wenn sie Temperaturen ausgesetzt werden, die über 30° C liegen, wobei das Ausmaß der Schädigung von der Einwirkungszeit abhängt. Deswegen ist es überaus wichtig, daß der Agar vor dem Gießen auf 42° C gekühlt wird. Die Abkühlungsrate des Agarmediums in den Platten wird von der Beschaffenheit und der Temperatur der Tischoberfläche, auf der die Platten stchen, beeinflußt.

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Plating the heterogeneous bacteria occuring naturally in samples of raw sea water with volumes of molten nutrient agar exceeding 10 ml reduces the number of colonies which develop. Plate counts on replicate samples of sea water are generally highest and results are more nearly reproducible when 10 ml of nutrient agar is used rather than volumes ranging randomly from 5 to 30 ml. Although other factors are involved, the adverse effects of volumes of nutrient agar appreciable larger than 10 ml are attributed primarily to the slower cooling rates during conventional plating procedures. When nutrient agar medium at 42° C was poured into pyrex Petri dishes at room temperature (22–24° C), 10 ml of the medium cooled to 30° C in about one minute, whereas from about 5 to 24 minutes were required for 20 to 50 ml of the medium to cool from 42° C down to 30 ° C. Many marine bacteria are injured by being subjected to temperatures higher than 30° C, the extent of the injury being a function of time. Therefore, it is of paramount importance that agar be cooled to 42° C prior to pouring. The rate at which agar medium cools in plates is influenced by the composition and temperature of the table top on which the plates rest.

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Contribution from the Scripps Institution of Oceanography, University of California, La Jolla, California.     

A review of length–weight relationships of fishes from freshwaters of Turkey

This paper presents 145 length–weight relationships gathered from the literature pertaining to 30 Turkish freshwater fish species belonging to six families. The value of the slope b ranged from 2.04 for Carassius carassius to 3.46 for Scardinus erythroptalmus. The mean value of b was 2.91 (SD = 0.305), which did not differ significantly from 3.0 (t‐test, P > 0.05). The median value of b was 2.95; 50% of the b values ranged from 2.68 to 3.14. The plot of log a vs b was used to detect outliers.     

Bacterial Abundance and the Activity of Microbiological Processes in the Bay of Tugur of the Sea of Okhotsk

This paper presents the results of investigation of the total abundance and the biomass of bacterioplankton, the abundance of heterotrophic bacteria, and the activity of microbiological processes involved in the carbon cycle in the water of the Bay of Tugur of the Sea of Okhotsk. In different regions of the bay, the total abundance of bacterioplankton was found to vary from 0.51 × 10⁶ to 2.54 × 10⁶ cells/ml; the bacterioplankton biomass, from 8.5 to 46.5 g C/l; the abundance of heterotrophic bacteria, from 0.06 × 10³ to 2.12 × 10³ cells/ml; the bacterial assimilation of CO₂, glucose, acetate, and protein hydrolysate, from 0.8 to 6.3, from 0.11 to 1.88, from 0.07 to 0.56, and from 0.01 to 0.22 mg C/(m³ day), respectively; the degradation of organic matter ranged from 28 to 221 mg C/(m³ day); and the intensity of methane oxidation, from 0.0005 to 0.17 l CH₄/l. The spatial pattern and the functional characteristics of bacterioplankton in the Bay of Tugur were found to be dependent on the tidal dynamics.     

Development of marker-free strains of Bacillus subtilis capable of secreting high levels of industrial enzymes

Different strategies have been employed to achieve high-level expression of single-copy genes encoding secreted enzymes in Bacillus subtilis. A model system was developed which utilizes the aprL gene from Bacillus clausii as a reporter gene for monitoring expression levels during stationary phase. An exceptionally strong promoter was constructed by altering the nuceotide sequence in the −10 and −35 regions of the promoter for the amyQ gene of Bacillus amyloliquefaciens. In addition, two or three tandem copies of this promoter were shown to increase expression levels substantially in comparison to the monomer promoter alone. Finally, the promoter and mRNA stabilization sequences derived from the cry3A gene of Bacillus thuringiensis were used in combination with the mutant amyQ promoter to achieve the highest levels of aprL expression. These promoters were shown to be fully functional in a high-expressing Bacillus strain grown under industrial fermentation conditions. The ability to obtain maximum expression levels from a single copy gene now makes it feasible to construct environmentally friendly, marker-free industrial strains of B. subtilis. Journal of Industrial Microbiology & Biotechnology (2000) 25, 204–212. Received 05 January 2000/ Accepted in revised form 26 June 2000     

Studies on the effects of subzero temperatures on the viability of spores of Aspergillus flavus. I. The effect of rate of warming

1. The survival of spores of Aspergillus flavus suspended in distilled water and cooled rapidly to –70 to –75°C. was found to depend primarily on the rate of subsequent warming of the frozen suspension. Only 7 per cent of the spores germinated following slow warming at 0.9°C. per minute, whereas about 75 per cent germinated following rapid warming at 700°C. per minute. 2. Viability was dependent on the rate at which the suspensions warmed from –70 to 0°C. (subzero warming), but was not dependent on the rate of thawing of the frozen water in which the spores were suspended. 3. The logarithm of the percentage of germination appeared to be a linear function of the logarithm of the rate of subzero warming when spores were warmed at rates ranging from 0.12 to 1000°C. per minute. 4. The lethal effects of slow warming from –70 to 0°C. were more pronounced between about –20 and 0°C. than between –70 and –20°C. In the former range of temperatures, the percentage of germination decreased sharply as slow warming progressed towards 0°C. 5. Slow warming from –70 to 0°C. was more harmful to the spores than was a 1 or 2 hour exposure to constant temperatures between –70 and 0°C. 6. Slow warming was found to be more harmful than rapid warming when spores were suspended in horse serum, 0.16 molal sodium chloride, or 0.29 molal sucrose as well as in distilled water.     

Absence of sodA Increases the Levels of Oxidation of Key Metabolic Determinants of Borrelia burgdorferi

Borrelia burgdorferi, the causative agent of Lyme disease, alters its gene expression in response to environmental signals unique to its tick vector or vertebrate hosts. B. burgdorferi carries one superoxide dismutase gene (sodA) capable of controlling intracellular superoxide levels. Previously, sodA was shown to be essential for infection of B. burgdorferi in the C3H/HeN model of Lyme disease. We employed two-dimensional electrophoresis (2-DE) and immunoblot analysis with antibodies specific to carbonylated proteins to identify targets that were differentially oxidized in the soluble fractions of the sodA mutant compared to its isogenic parental control strain following treatment with an endogenous superoxide generator, methyl viologen (MV, paraquat). HPLC-ESI-MS/MS analysis of oxidized proteins revealed that several proteins of the glycolytic pathway (BB0057, BB0020, BB0348) exhibited increased carbonylation in the sodA mutant treated with MV. Levels of ATP and NAD/NADH were reduced in the sodA mutant compared with the parental strain following treatment with MV and could be attributed to increased levels of oxidation of proteins of the glycolytic pathway. In addition, a chaperone, HtpG (BB0560), and outer surface protein A (OspA, BBA15) were also observed to be oxidized in the sodA mutant. Immunoblot analysis revealed reduced levels of Outer surface protein C (OspC), Decorin binding protein A (DbpA), fibronectin binding protein (BBK32), RpoS and BosR in the sodA mutant compared to the control strains. Viable sodA mutant spirochetes could not be recovered from both gp91/phox ^−⁄− and iNOS deficient mice while borrelial DNA was detected in multiple tissues samples from infected mice at significantly lower levels compared to the parental strain. Taken together, these observations indicate that the increased oxidation of select borrelial determinants and reduced levels of critical pathogenesis-associated lipoproteins contribute to the in vivo deficit of the sodA mutant in the mouse model of Lyme disease. This study, utilizing the sodA mutant, has provided insights into adaptive capabilities critical for survival of B. burgdorferi in its hosts.     

Chemistry of the “molecular trap” of protease-catalyzed splicing reaction of complementary segments of α-subunit of hemoglobin A

The complementary fragments of human Hb α, α_1–30, and α_31–141 are spliced together by V8 protease in the presence of 30%n-propanol to generate the full-length molecule (Hb α-semisynthetic reaction). Unlike the other protease-catalyzed protein/peptide splicing reactions of fragment complementing systems, the enzymic condensation of nonassociating segments of Hb α is facilitated by the organic cosolvent induced α-helical conformation of product acting as the “molecular trap” of the splicing reaction. The segments α_24–30 and α_31–40 are the shortest complementary segments that can be spliced by V8 protease. In the present study, the chemistry of the contiguous segment (product) α_24–40 has been manipulated by engineering the amino acid replacements to the positions α²⁷ and α³¹ to delineate the structural basis of the molecular trap. The location of Glu²⁷ and Arg³¹ residues in the contiguous segment α_24–40 (as well as in other larger segments) is ideal to generate (i, i+4) side-chain carboxylate-guanidino interaction in its α-helical conformation. The amino acid residue replacement studies have confirmed that the side chains at α²⁷ and α³¹ facilitate the semisynthetic reaction. The relative influence of the substitute at these sites on the splicing reaction depends on the chemical nature of the side chain and the location. The γ-carboxylate guanidino side-chain interaction appears to contribute up to a maximum of 85% of the thermodynamic stability of the molecular trap. The studies also demonstrate that the thermodynamic stability of the molecular trap is determined by two interdependent conformational aspects of the peptide. One is an amino acid-sequence-specific event that facilitates the induction of an α-helical conformation to the contiguous segment in the presence of organic cosolvent that imparts some amount of protease resistance to Glu³⁰-Arg³¹ peptide bond. The second structural aspect is a site-specific event, ani, i+4 side-chain interaction in the α-helical conformation of the peptide which imparts an additional thermodynamic stability to the molecular trap. The results suggest that conformationally driven “molecular traps” of protease-mediated ligation reactions of peptides could be designed into products to facilitate the modular assembly of peptides/proteins.     

Contraction of protoplasm. III. Cinematographic analysis of the contraction of some heterotrichs

The contraction of Stentor and Blepharisma, in response to mechanical and electrical stimulation and of Spirostomum in response to mechanical stimulation is described. All three species respond to electrical stimulation by contraction of the cytoplasm, beginning at the anodal end regardless of orientation of the animal. The differences in contractile ability and shapes during contraction are discussed in relation to body form and microanatomy. Stentor and Spirostomum also respond to mechanical stimulation. Dropping a weight on the slide causes contraction of the whole body of Spirostomum, but not of Stentor. Stimulation of the oral region of Stentor by means of a vibrating needle causes a contraction of the entire body, but this sensitivity is limited to the oral region. Blepharisma does not respond to mechanical stimulation. Spirostomum and Stentor undergo rapid spontaneous contractions, but Blepharisma does not contract spontaneously.     

Identification of Sources of Resistance to Four Species of Root-knot Nematodes in Tobacco

Resistance to the southern root-knot nematode, Meloidogyne incognita races 1 and 3, has been identified, incorporated, and deployed into commercial cultivars of tobacco, Nicotiana tabacum. Cultivars with resistance to other economically important root-knot nematode species attacking tobacco, M. arenaria, M. hapla, M. javanica, and other host-specific races of M. incognita, are not available in the United States. Twenty-eight tobacco genotypes of diverse origin and two standard cultivars, NC 2326 (susceptible) and Speight G 28 (resistant to M. incognita races 1 and 3), were screened for resistance to eight root-knot nematode populations of North Carolina origin. Based on root gall indices at 8 to 12 weeks after inoculation, all genotypes except NC 2326 and Okinawa were resistant to M. arenaria race 1, and races 1 and 3 of M. incognita. Except for slight root galling, genotypes resistant to M. arenaria race 1 responded similarly to races 1 and 3 of M. incognita. All genotypes except NC 2326, Okinawa, and Speight G 28 showed resistance to M. javanica. Okinawa, while supporting lower reproduction of M. javanica than NC 2326, was rated as moderately susceptible. Tobacco breeding lines 81-R-617A, 81-RL- 2K, SA 1213, SA 1214, SA 1223, and SA 1224 were resistant to M. arenaria race 2, and thus may be used as sources of resistance to this pathogen. No resistance to M. hapla and only moderate resistance to races 2 and 4 of M. incognita were found in any of the tobacco genotypes. Under natural field infestations of M. arenaria race 2, nematode development on resistant tobacco breeding lines 81-RL-2K, SA 1214, and SA 1215 was similar to a susceptible cultivar with some nematicide treatments; however, quantity and quality of yield were inferior compared to K 326 plus nematicides.     

Effects of hormones and inhibitors of macromolecular synthesis on the follicle cells of Rhodnius

The response of the follicle cells of Rhodnius prolixus to JH in vitro was found to be independent of de novo macromolecular synthesis as exemplified by the failure of Actinomycin D, and puromycin to inhibit the response at any but the highest concentrations employed. C₁₈ JH was found to be a more effective gonadotropin than C₁₆ JH in this in vitro study. Neither methyl palmitate nor ecdysone mimiced or antagonised the action of JH on the follicle cells in vitro. Follicle cells of ovaries removed from allatectomised mated females failed to respond to C₁₆ JH and ecdysone in vitro.     

The effect of low levels of carbon dioxide on metabolism of Mus musculus

• 1.1. In this study we measured the metabolic response of individual mice to low concentrations of carbon dioxide in air (0.14 to 1.7%). Both oxygen consumption (V_o2) and carbon dioxide (V_o2) were determined, and the respiratory quotient (R) was calculated.
• 2.2. V_o2 was significantly reduced at levels of 0.14 to 0.50% CO₂ in the air. At 0.23% for example, V_o2 dropped from 3.11 ± 0.6 to 1.26 ± 0.69 cc O₂/g × hr. R increased from 0.7 to 1.0 and higher throughout the 6-hr testing period, which consisted of 1.5 hr of exposure to 0.0% CO₂, 1.5 hr of exposure to a test gas and a repetition of 1.5 hr each of baseline and test exposures.
• 3.3. We conclude that low levels of CO₂ such as mice might encounter in a nest, burrow or even metabolic chamber may effect a feedback mechanism which acts to decrease metabolism.

     

Mechanism of activation of Xenopus CFTR by stimulation of PKC

PKA-mediated phosphorylation of the regulatory (R) domain plays a major role in the activation of the human cystic fibrosis transmembrane conductance regulator (hCFTR). In contrast, the effect of PKC-mediated phosphorylation is controversial, smaller than that of PKA, and dependent on the cell type. In the present study, we expressed Xenopus CFTR (XCFTR) and hCFTR in Xenopus oocytes and examined their responses (i.e., macroscopic membrane conductance) to maximal stimulation by PKC and PKA agonists. With XCFTR, the average response to PKC was approximately sixfold that of PKA stimulation. In contrast, with hCFTR, the response to PKC was 90% of the response to PKA stimulation. The reason for these differences was the small response of XCFTR to PKA stimulation. Using the substituted cysteine accessibility method, we found no evidence for insertion of functional CFTR channels in the plasma membrane in response to PKC stimulation. The increase in macroscopic conductance in response to PKC stimulation of XCFTR was due to an approximately fivefold increase in single-channel open probability, with a minor (30%) increase in single-channel conductance. The responses of XCFTR to PKC stimulation and of hCFTR to PKA stimulation were mediated by similar increases in P_o. In both instances, there were no changes in the number of channels in the membrane. We speculate that in animals other than humans, PKC stimulation may be the dominant mechanism for activation of CFTR. chloride channel; channel regulation; cystic fibrosis transmembrane conductance regulator gating; cystic fibrosis; phosphorylation; protein kinase A     

Characterization of the RpoS Status of Clinical Isolates of Salmonella enterica

The stationary-phase-inducible sigma factor, σ^S (RpoS), is the master regulator of the general stress response in Salmonella and is required for virulence in mice. rpoS mutants can frequently be isolated from highly passaged laboratory strains of Salmonella. We examined the rpoS status of 116 human clinical isolates of Salmonella, including 41 Salmonella enterica serotype Typhi strains isolated from blood, 38 S. enterica serotype Typhimurium strains isolated from blood, and 37 Salmonella serotype Typhimurium strains isolated from feces. We examined the abilities of these strains to produce the σ^S protein, to express RpoS-dependent catalase activity, and to resist to oxidative stress in the stationary phase of growth. We also carried out complementation experiments with a cloned wild-type rpoS gene. Our results showed that 15 of the 41 Salmonella serotype Typhi isolates were defective in RpoS. We sequenced the rpoS allele of 12 strains. This led to identification of small insertions, deletions, and point mutations resulting in premature stop codons or affecting regions 1 and 2 of σ^S, showing that the rpoS mutations are not clonal. Thus, mutant rpoS alleles can be found in freshly isolated clinical strains of Salmonella serotype Typhi, and they may affect virulence properties. Interestingly however, no rpoS mutants were found among the 75 Salmonella serotype Typhimurium isolates. Strains that differed in catalase activity and resistance to hydrogen peroxide were found, but the differences were not linked to the rpoS status. This suggests that Salmonella serotype Typhimurium rpoS mutants are counterselected because rpoS plays a role in the pathogenesis of Salmonella serotype Typhimurium in humans or in the transmission cycle of the disease.     

Specificity of interplant cycling of phosphorus: The role of mycorrhizas

The cycling of nutrients from dying roots of one plant (the donor) to other intact plants (the receivers) was examined in a series of pot experiments. In each pot receiver plants formed either the same or a different type of mycorrhiza as the donor plant and was therefore respectively either capable or incapable of forming mycorrhizal hyphal links to the donor. There was a preferential transfer of ³²P from the dying roots of the vesicular-arbuscular mycorrhizal (VAM) Lolium perenne to VAM-infected trees Acer pseudoplatanus and Fraxinus excelsior compared to the ectomycorrhizal (ECM) Larix eurolepis, this despite an apparently greater competitive ability of L. eurolepis to obtain ³²P from the soil. Following the death of L. perenne roots there was also an increase in total P in the VAM tree receiver. These findings could not be explained by similarities in rooting distribution of the VAM-infected plants.In a similar study of the transfer of ³²P between heathland plants there was a preferential cycling of ³²P from one ericoid mycorrhizal Calluna vulgaris to another rather than to the VAM Molinia caerulea. In contrast, when ³²P was supplied directly to the soil, M. caerulea obtained significantly more ³²P than C. vulgaris. These results are discussed in relation to the potential role of interplant mycorrhizal links in the cycling of nutrients within partially closed cycles and the implications that this might have for species balance in plant communities.     

Kinetics of the reversible association of ribosomal subunits: Stopped-flow studies of the rate law and of the effect of Mg2+

The kinetics of association and dissociation of Escherichia coli 30 S and 50 S ribosomal subunits appear to fit the simple scheme

over a wide range of Mg²⁺ and ribosome concentrations, for the preparations studied (which have a sharp [Mg²⁺]-dependence on the equilibrium degree of association, e.g. 10% to 90% for 1.5 mm to 3.5 mm). Both rate constants depend strongly upon magnesium ion concentration (k₂ goes from 0.04 × 10⁶ to 21 × 10⁶m⁻¹ s⁻¹ as [Mg²⁺] goes from 1.5 mm to 8 mm; k₁ goes from 150 to 2 s⁻¹ in the interval 1.0 to 3.0 mm), but k₁ may level off above 3.0 mm and k₂ increases slowly at high [Mg²⁺]. (The highest rate may not be far from the diffusion-controlled limit.) The primary effect of Mg²⁺, as calculated from the rather large changes in binding as a function of [Mg²⁺], is to decrease the contribution of electrostatic repulsion to the free energy of activation; specific, or class-specific, interactions of di- and multivalent cations with unknown ribosomal substructures may modulate this effect.     

非计划再次手术关键环节管理与效果分析

目的 探索有效降低非计划再次手术发生率的管理方法。方法 对2012年1月—2016年12月住院并进行手术的患者进行主动监测,加强管理,发现非计划再次手术病例,统计发生率及引发原因。结果 225 944例手术共发生非计划再次手术914例,平均发生率为0.40%且五年呈显著下降趋势。引发原因以手术部位感染、切口裂开、切口疝或愈合不良,术后出血,出现漏或瘘为主,共占73.9%。结论 完善主动监测与报告系统、加强院科两级管理、注重原因分析与改进可有效降低非计划再次手术的发生率。