发网菌目黏菌子实体微量元素的初步分析

运用能散X-射线微区分析技术研究了发网菌目黏菌代表种的子实体的微量元素组成,结果表明:分属于7属的7种供试发网黏菌子实体囊被上的微量元素组成存在差异。尽管在显微镜下观察不到可见的如绒泡菌目黏菌子实体中存在的石灰质颗粒,但其中的钙元素所占比例均仍较高。同时,元素组成上的差异与子实体的颜色没有相关性。     

A critical reevaluation of some assay methods for superoxide dismutase activity

We have compared the direct method of pulse radiolysis to the indirect methods of cytochrome c and nitroblue tetrazolium for assaying the superoxide dismutase activity of a compound. We have shown that with pulse radiolysis, where high concentrations of O2- are generated, the "turnover" rate constant, kcat, can be determined directly, while with the indirect methods, where relatively low steady state concentrations of O2- are formed, the value of kcat determined by these methods, can be orders of magnitude lower than that determined directly. The main reason for the lower values obtained with the indirect methods is due to the fast reoxidation of the reduced compound by molecular oxygen. Additional problems which arise with the use of indirect methods for determining superoxide dismutase catalytic activity are discussed.     

A critical examination of some histochemical methods for demonstrating tetrahydrofolate dehydrogenase

Synopsis Two different methods, one proposed by us (1969, 1970) and the other by Onicescuet al. (1970), for the histochemical demonstration of tetrahydrofolate dehydrogenase have been compared using as test materials frozen sections of mouse liver and blood smears of laboratory animals that had been infected experimentally with malaria.Our method appears to be of practical value, especially for blood smears. It is based on the following principles: (a) the enzymic reaction proceeds via the reduction of the pyridine coenzyme NADP by tetrahydrofolic acid (dissolved in 2-mercaptoethanol to prevent its spontaneous oxidation); (b) an intermediate electron carrier, phenazine methosulphate, is used to increase the reaction sensitivity; and (c) antifolate metabolic inhibitors are added in specificity controls.The differences between other methods, which have failed in our hands, and our method are discussed critically.Centre for the Study of Histochemistry of the C.N.R.     

A chemosystematic study of some geraniaceae

The flavonoids of five Geranium, fourteen Erodium and four Monsonia species were studied. Quercetin was the most common aglycone with lesse     

A critical look at some widely used estimators in mark-resighting experiments

1. For many species and circumstances, mark-resighting procedures constitute valid alternatives to capture-recapture methods. Indeed, resightings are generally cheaper to acquire than physically recapturing and rehandling the animals, especially when radiotelemetry or other tracking devices are available. 2. In order to estimate population abundance, the joint hypergeometric maximum likelihood estimator, the Minta-Mangel estimator and the Bowden estimator are implemented in noremark, software which has become very popular with biologists in the past decade. 3. In this paper, the basic assumptions regarding these widely applied procedures are delineated and discussed. A simulation study is performed in order to investigate the robustness of the estimators under failure of the assumptions. 4. Theoretical considerations and simulation results motivate the use of the Bowden estimator which, when marks are distributed quite evenly among groups, constitutes the sole reliable method, offering computational simplicity and robustness. On the other hand, if the marks are distributed unevenly, no mark-resighting procedure seems reliable. An application to a case study is considered.     

A taxonomic review of the nivicolous species of myxomycetes described by Kowalski. I. Order Stemonitales

Five type specimens of species from the order Stemonitales proposed by Kowalski are re-examined. These are Comatricha fusiforme, Diacheopsis effusa, D. serpula, Lamproderma acanthosporum and L. disseminatum. SEM and LM micrographs of spores, capillitia and sporocarps are provided. Critical study of these type specimens supports Kowalski’s recognition of these taxa as good and valid species.     

A critical study of the taxonomic value of some tests of assimilation used for the classification of the sporogenous yeasts

Six texts of assimilation used in the taxonomy of yeasts, (lactose, maltose, cellobiose, trehalose, melibiose, sucrose) have been critically tested by the examination of intracellular enzymic systems. The results obtained among the sporogenous species ofSaccharomyces, Kluyveromyces, Pichia, Hansenula, Debaryomyces indicate that cellobiose, lactose, maltose and trehalose tests no longer supply an important value for the speciation, because the number of cryptical osidases is so high.     

Characterisation of engineered proteins: some critical reflections

This essay is an attempt to point up the gap between, on the one hand, the methods currently available to the biologist in the laboratory and, on the other, the kind of data that he or she would need in order to characterise genetically engineered proteins of topical biological interest in such a way as to make use of the techniques of protein engineering.     

A critical distance study of stress concentrations in bone

The Theory of Critical Distances (TCD) is a method used to study the failure of material in situations where stress concentrations, such as holes and notches, are present. This method uses two material constants: a critical length and a critical stress. The elastic stress field close to the stress concentration is examined, applying a fracture criterion. The TCD has been applied to predict brittle fracture in various different materials and various types of notches but it has not previously been applied to bone. Since bone fails by brittle fracture with limited plasticity, it is expected that the TCD will be applicable. Experimental data were obtained from the literature on the effects of sharp notches and holes loaded in various ways (tension, torsion and bending). These tests were modelled using finite element analysis. It was found that the TCD could be successfully applied to predict the load required for brittle fracture as a function of the type and size of the stress concentration feature. The critical distance was found to be almost constant, about 0.3-0.4mm, for all types of bone studied: the critical stress was found to be related to the material's ultimate tensile strength by a constant factor of T=1.33. The results of this study will be of practical value in the assessment of stress concentration features introduced during surgery and of naturally occurring bone defects.     

The oxidative cleavage of folates. A critical study

Alkaline permanganate oxidation has been used to determine the chain length of naturally occurring pteroylpolyglutamates on the assumption that all forms of folates cleave at the C⁹N¹⁰ bond to produce the corresponding p-aminobenzoyl-polyglutamates. The chain length of the latter could be determined by cochromatography with synthetic markers. The products of alkalinc (ammonium bicarbonate buffer, pH 9.0) permanganate oxidation of a number of reduced and oxidized, one-carbon-substituted and unsubstituted folic acid derivatives have been identified, and their yields and stability to the oxidative treatment have been determined. Unsubstituted, oxidized and reduced folic acid and N⁵-formyl-tetrahydrofolic acid are cleaved at the C⁹N¹⁰ bond to produce p-aminobenzoylglutamic acid. N⁵, N¹⁰-methenyl-tetrahydrofolic acid, N⁵,N¹⁰-methylene-tetrahydrofolic acid, and N¹⁰-formyl-tetrahydrofolic acid are not cleaved but are oxidized to N¹⁰-formyl-folic acid which is completely stable to the oxidative treatment employed. N⁵-methyl-tetrahydrofolic acid is not cleaved either but is oxidized to N⁵-methyl-dihydrofolic acid which upon continued oxidation decomposes slowly to unidentified products. The γ-glutamyl peptide linkage is completely stable to oxidation. Using p-amino-[3,5-³H]benzoylglutamic acid, it is also shown that this product, previously thought to be stable to the oxidative treatment is decomposed by it. The significance of these findings in terms of the errors that may have been introduced in prior estimations of the chain length and pool sizes of the naturally occurring pteroylpolyglutamates is discussed. The possibility of developing a method for the chain length determination of noncleavable pools of one-carbon-substituted folates using [2-¹⁴C]folic acid to label the folates in vivo is presented.     

A study of some factors influencing amylose gelation

Amylose fractions were prepared by aqueous leaching from pea, maize and patato starch granules. The fractions were characterised by iodine binding, β-amylolysis and viscometry. Amylose starts to form a gel rather than a precipitate on cooling aqueous solutions to room temperature at concentrations above the coil overlap concentration C¹. Amylose gels are almost purely elastic, with negligible viscous flow at room temperature. The rigidity modulus is strongly dependent on concentration, c, in that above 1·5% w/w the modulus increases as a function of c⁷. The modulus of a matured gel falls only slightly with increasing temperature; at temperatures below 100°C the gel could not be melted. The non-equilibrium nature of the system is shown by the dependence of rigidity on thermal history. The shear modulus is also dependent on amylose type; higher molecular weight amylose fractions produced less rigid gels at a given concentration.