The secretion of amylase, phospholipase and protease from Aeromonas salmonicida, and the correlation with membrane-associated ribosomes

Abstract. The following extracellular enzymes have been readily detected in the culture filtrates from Aeromonas salmonicida: amylase, phospholipase, lysophospholipase and ribonuclease. Amylase and phospholipase have been partially characterized. Evidence suggests that glycogen may be the natural substrate for amylase, and that the role of the enzyme in natural infection is to digest glycogen present in fish muscle. The secretion of amylase activity is suppressed by the addition of glucose to the growth medium. The amounts of amylase, phospholipase and protease that can be detected in culture filtrates decreases with increase in the growth temperature from 25 to 32°C. This marked decrease in secretion of hydrolytic enzymes occurs although the initial growth rates at 25 and 32°C are similar. Free and membrane associated ribosomes have been isolated from cultures grown at 25 and 32°C. At 32°C there is a smaller proportion of membrane-associated ribosomes and this is consistent with the hypothesis that extracellular enzymes from Aeromonas salmonicida are secreted on membrane-bound polysomes.     

Proteases secreted by strains of Aeromonas salmonicida

Abstract. The proteases secreted by four strains (MT004, 1102, 480 and 480P^-) of Aeromonas salmonicida grown in liquid culture have been studied. Strains MT004, 1102 and 480 all show a similar pattern with two types of proteases produced; one of molecular weight 70 000 which is active against casein and gelatin and one (or more) of lower molecular weight (about 20 000) which is (are) active against gelatin but not casein. Strain 480P^- produces only the latter type of protease(s). The protease of molecular weight 70 000 is classified as a serine-type protease, but further characterization of the features of its active site has not yet proved possible. The results are discussed in terms of the previously published but often contradictory data on the proteases of A. salmonicida.     

关于内蒙古大兴安岭林区大径材培育的探讨

文章通过对内蒙古大兴安岭林区培育大径材的目的、意义、必要性及方法等方面的分析,论述了大径级材培育是促进林区生态、经济和社会协调发展的有力措施。     

Isotopic fractionation of stratospheric nitrous oxide

We propose an isotopic fractionation mechanism, based on photolytic destruction, to explain the 15N/14N and 18O/16O fractionation of stratospheric nitrous oxide (N2O) and reconcile laboratory experiments with atmospheric observations. The theory predicts that (i) the isotopomers 15N14N16O and 14N15N16O have very different isotopic fractionations in the stratosphere, and (ii) laboratory photolysis experiments conducted at 205 nanometers should better simulate the observed isotopic fractionation of stratospheric N2O. Modeling results indicate that there is no compelling reason to invoke a significant chemical source of N2O in the middle atmosphere and that individual N2O isotopomers might be useful tracers of stratospheric air parcel motion.     

SOIL CORROSIVENESS IN SOUTH OXFORDSHIRE

The potential corrosiveness of four soil series was studied in south Oxfordshire by measuring soil properties (resistivity, pH, sulphate content, moisture content and redox potential) thought to be closely connected with ferrous metal corrosion. Fifty random points were located in areas of the soil series map units. Paired measurements of resistivity were made at each sampling point. Analysis of variance over all groups (soil map units) showed that, for all properties except redox potential, between group variance exceeded within group variance. The amount of variance contributed from within the pairs of resistivity measurements was small suggesting little short range variation in this property. There was good association between the properties measured and the soil map units. The kinds of soil identified and the delineations on the soil map therefore represents a useful partitioning of the areas studied in terms of corrosion risk.     

Optical studies of individual InAs quantum dots in GaAs: few-particle effects

Optical emission from individual strained indium arsenide (InAs) islands buried in gallium arsenide (GaAs) was studied. At low excitation power density, the spectra from these quantum dots consist of a single line. At higher excitation power density, additional emission lines appeared at both higher and lower energies, separated from the main line by about 1 millielectron volt. At even higher excitation power density, this set of lines was replaced by a broad emission peaking below the original line. The splittings were an order of magnitude smaller than the lowest single-electron or single-hole excited state energies, indicating that the fine structure results from few-particle interactions in the dot. Calculations of few-particle effects give splittings of the observed magnitude.     

Morpho‐physical Recording of Bovine Conceptus (Bos indicus) and Placenta from Days 20 to 70 of Pregnancy

The study is based on 141 pregnant Bos indicus cows, from days 20 to 70 post‐insemination. First, special attention was given to the macroscopically observable phenomena of attachment of the conceptus to the uterus, i.e. the implantation, from about days 20 to 30 post‐insemination up to day 70, and placentome development by growth, vascularization and increase in the number of cotyledons opposite to the endometrial caruncles. Secondly, as for the conceptuses, semiquantitative, statistical analyses were performed of the lengths of chorio‐allantois, amnion and yolk sac; and the different parts of the centre and two extremes of the yolk sacs were also analysed. Thirdly, the embryos/foetuses corresponding to their membranes were measured by their greatest length and by weight, and described by the appearance of external developmental phenomena during the investigated period like neurulation, somites, branchial arcs, brain vesicles, limb buds, C‐form, pigmented eye and facial grooves. In conclusion, all the data collected in this study from days 20 to 70 of bovine pregnancy were compared extensively with corresponding data of the literature. This resulted in an ‘embryo/foetal age‐scale’, which has extended the data in the literature by covering the first 8 to 70 days of pregnancy. This age‐scale of early bovine intrauterine development provides model for studies, even when using slaughtered cows without distinct knowledge of insemination or fertilization time, through macroscopic techniques. This distinctly facilitates research into the cow, which is now being widely used as ‘an experimental animal’ for testing new techniques of reproduction like in vitro fertilization, embryo transfer and cloning.