Murein hydrolase (N-acetyl-muramyl-l-alanine amidase) in human serum

An enzyme was identified in human serum which unlike lysozyme cleaved the amide bond between N-acetyl-muramic acid and l-alanine of the peptide side chain of the rigid layer (murein) of Escherichia coli. The N-acetylmuramyl-l-alanine amidase released all of the peptide side chains including those to which the lipoprotein is bound. A portion of the peptide side chains of the Micrococcus lysodeikticus murein was also hydrolysed from the polysaccharide chains. E. coli, M. lysodeikticus, Bacillus subtilis and Staphylococcus aureus were not killed by the amidase. Treatment of E. coli with EDTA or osmotic shock rendered the cells sensitive to the amidase and they were killed. Possible biological functions of the amidase are discussed.The enzyme was separated from lysozyme in human serum. Gel permeation chromatography indicated a molecular weight of the active enzyme of 82,000 while gel electrophoresis in the presence of sodium dodecyl sulfate revealed a molecular weight of 75,000. Thus, the enzyme probably consists of a single polypeptide chain. Incubation with neuraminidase rendered the amidase more basic suggesting the release of sialic acid residues. The modified glycoprotein disclosed an increased activity to murein. Enzyme activity was inhibited by p-chloromercuribenzene sulfonate and ethyleneglycol-bis(2-aminomethyl) tetraacetate (EGTA) at 1 and 0.2 mM concentration, respectively, whereas EDTA up to 5 mM was without effect. The amidase was also inactivated by agents that reduce disulfide bridges.     

Host-attacking behavior of a eulophid parasite,Kratochviliana sp., to the leaf mining host,Phytomyza ranunculi (Diptera: Agromyzidae) during its stay on the leaf

The present paper studies how the female parasite of Kratochviliana sp. visits and attacks its host larvae of Ranunculus leaf mining fly, P. ranunculi at a single leaf visit. The parasite visited its hosts at random on the leaf. The frequency of host visits was independent of the host density and the proportion of hosts survived from the parasite attack, in a leaf and its distribution was expressed as a single straight line. It almost always attacked living hosts at the first host visit after isolated from them for one day but with the rate of about 0.5 at the subsequent visits. In consequence, the relationships of the number of host attacks and killed hosts to the host density drew satulated curves in each. A model of host attack by this parasite at its single leaf visit was formulated by modifyingBakker et al.'s model (1972) basing upon these observations and the attack avoidance by the parasite to already attacked hosts previously reported.     

Analysis of picogram quantities of indole-3-acetic acid by high performance liquid chromatography-fluorescence procedures

The use of spectrofluorimeter coupled to a reverse phase high performance liquid chromatography column permits selective detection of indole-3-acetic acid at the low picogram level. The value of the technique is demonstrated by the analysis of endogenous IAA in elongating shoots, xylem sap and callus of Douglas-fir. The data are also used to illustrate a procedure whereby the accuracy of chromatographic analyses can be verified within definable probability limits.Abbreviations GC-MS combined gas chromatography-mass spectrometry - HPLC high performance liquid chromatography - IAA indole-3-acetic acid - SEC steric exclusion chromatography - SICM selected ion current monitoring Technical Paper No. 5379 from the Oregon State University Agricultural Experiment Station     

Effects of nitrogen deficiency and light of high intensity onCryptomonas rufescens (Cryptophyceae)

Summary C.rufescens excystment, experimentally induced, corresponds to a general metabolism recovery of the cell, previously in a resting phase. The cytoplasm changes without any polarity, and organelles like gullet and flagella redifferentiate. The thylakoids develop mainly from the stored lipidic compounds which then disappear. Phycoerythrin immediately fills the intrathylakoidal lumen. Pigment synthesis seems closely associated with the development of membranes. The activated cell divides and the cyst wall breaks down. The destruction of the wall begins in the median layer and is followed by a mechanical rupture of the external and internal layers. Each germinative cyst releases two or four fully differentiated cells. There is an exact symmetry between excystment and encystment, all the transformations of theC. rufescens cell being reversible.     

Characterization of a new murein-associated lipoprotein in the outer membrane of Proteus mirabilis

A murein-associated outer membrane protein from Proteus mirabilis has been isolated. Since the protein carries ester- as well as amide-linked fatty acids it can be classified as a second outer membrane lipoprotein. An apparent molecular weight of 15,000 for this protein was determined from amino acid analysis and sodium dodecylsulfate/polyacrylamide gel electrophoresis. The amino acid composition, however, does not show similarities with the amino acid composition of the lipoprotein covalently linked to murein, which has a molecular weight of 7,300 as described previously in Proteus mirabilis.Abbreviation SDS sodium dodecylsulfate     

Fractionation of plant protoplast types by iso-osmotic density gradient centrifugation

Summary A simple effective technique for the fractionation of protoplast populations is described. Protoplasts are separated by low-speed centrifugation in an iso-osmotic, discontinuous density gradient system on the basis of differences in their buoyant densities. At a constant osmolality of 660±20 mOs/kg H₂O, the gradients provide a density range from 1.017 to 1.069 g/cm³ at 20 °C which corresponds to the buoyant densities of most protoplast types studied. Characteristics of the KMC/S-density gradient system and factors affecting the fractionation were investigated. Protoplasts were isolated from various tissues and cultivars of tobacco, barley, wheat, rye, oat and maize. Their density-dependent distribution profiles in KMC/S-gradients and their average buoyant densities were determined under standardized conditions. Great differences in the buoyant densities were found between protoplasts of different tissues. Mixed populations of two types of protoplasts, differing in buoyant density by about 15–20 mg/cm³, were separated to give highly purified fractions. Factors affecting the buoyant densities of protoplasts have been investigated. Ploidy level and species differences did not significantly affect the fractionation profiles. However, an age-dependent variation in the average buoyant density of tobacco mesophyll protoplasts was observed. Fractionation of tobacco mesophyll protoplasts and their subsequent regeneration to plants demonstrates the practicability and physiological compatibility of the KMC/S-density gradient system under sterile conditions. The morphogenetic potential of protoplasts was not affected by the separation procedure or the gradient components.     

Differentiation under the control of insulin of rat preadipocytes in primary culture: Isolation of homogeneous cellular fractions by gradient centrifugation

Using a density gradient medium (Percoll) we succeeded in isolating homogeneous cell populations from the stromal-vascular fraction of the inguinal tissue of 3-day-old rats. In primary culture, in medium 199 supplemented with 10% fetal calf serum and 5.5 mM glucose, almost complete differentiation (90%) of these fractions was obtained for the first time in presence of a physiological concentration of insulin (10^?9 M). During the adipose conversion, insulin markedly enhanced the activities of glycerol-3-phosphate dehydrogenase and acid:CoA ligase. When VLDL and heparin were added with insulin to the medium, this effect was not potentiated. On the contrary, VLDL and heparin in presence of insulin increased the triglyceride content of the cells. With VLDL and heparin only, the biochemical and morphological characteristics of the cells were very similar to those observed in control culture. The heavier fraction was morphologically heterogeneous and did not undergo the adipose conversion to the same extent as the two lighter fractions. It was concluded that this model could be helpful in studying the proliferation and the differentiation of preadipocytes at an early stage of development.     

高效液相层析法纯化人胎盘谷胱甘肽硫转移酶

足月分娩的新鲜胎盘组织制成匀浆后,经高速离心、超速离心,谷胱甘肽(GSH)Sepharose 6B亲合层析,Amicon pM-10膜超过滤及高效液相层析,最终经SDS-PAGE鉴定,结果呈现单一亚基区带,其亚基分子量为25000。 根据我们现有高效液相设备条件,用ODS柱代替RadulovicL等报道的特异阴离子柱,用磷酸盐洗脱液代替含谷胱甘肽、二硫苏糖醇及氯化钾的梯度洗脱液,从人胎盘组织成功地制备了谷胱甘肽硫转移酶(GST)纯酶,全过程在15min内完成,保留时间及主峰面积的重复性均较理想,7次实验结果的变异系数为0.2％,最终纯化578.9倍。本研究为各种形式GST的纯化制备提供了一个新的、重复性好、分辨率高及回收理想的简易方法。     

The influence of coppicing on vegetation

In the Netherlands and adjacent countries on old (non-holocene) soils the relation was studied between high forest dominated by Fagus sylvatica, and coppice derived from it, with Quercus spp. and Betula spp. or Carpinus betulus. From place-names a shift Fagus > Quercus > Betula is found, caused by cutting and coppicing. An analysis of relevés of the vegetation yielded more detailed information.The occurrence and rejuvenation of Fagus and other climax tree species decrease, while most other trees and shrubs show an increase. The mean total number of species in 1396 relevés increases from 22.0 to 24.4. Decreasing species include widely distributed species as well as character species. Increasing species include shrubs, woodedge species of heathland or limestone grassland, and nitrophilous species.The light-indication according to Ellenberg increases considerably, most of all in the types on poor soils. Moisture seems hardly involved, but pH-indication is divergent: decreasing in acid types, increasing in alkaline types. For the latter erosion is held responsible. N-indication follows the same trend. All ecological shifts remain within the framework of each association concerned.The Sørensen index for floristic composition shows a mean of 68% correlation, of the same order as variants within one association. The ecological correlation is even higher. So coppice can be considered as management variants, not deserving an association status, as often was given in the past.