Showing papers by "Université catholique de Louvain published in 1977"

Incompatibility in Angiosperms

Abstract: Since Darwinian times considerable knowledge has accumulated on the distribution, physiology and genetics of self-incompatibility (SI) in higher plants, In the second half of this century the first attempts were made to identify the biochemical bases of SI. These included the discovery that cutinase enables pollen tube penetration at the surface of the stigma in Cruciferae, sorting of segregation pollen S-phenotypes by serological techniques, a lock-and-key model of the SI reaction, the first detection and characterisation of SI proteins and the discovery of the role of the tapetum in the determination of pollen phenotypes in homomorphic sporophytic SI. This pioneering work was followed by a worldwide effort to identify and understand the cellular and molecular processes which lead to the recognition and rejection of SI pollen. The present review article summarizes briefly the current state of knowledge in areas essential for the understanding and exploitation of SI and outlines new information that has become available during recent years.

A Min-Max Relation for Submodular Functions on Graphs

Abstract: Publisher Summary This chapter describes a min-max relation for submodular functions on graphs. It proves a new combinatorial min-max equality that unifies and extends results including the matroid intersection theorem and the theorem of Lucchesi and Younger on the minimum number of edges, which meet every directed cut in a graph. The method of proof used in the chapter generalizes the method used to prove the polymatroid intersection theorem and the method used to prove the Lucchesi-Younger Theorem including an idea that Lovasz attributes to Neil Robertson.

Support for the astronomical theory of climatic change

Abstract: The quasi-periods of climatic variation found by Hays et al. (Science, vol.194, p.1121 (1976)) from deep-sea cores are examined. It is shown that these periods are very close to those predicted from the variations of the various `Milankovitch' parameters: the 24000 yr and 19500 yr periods from the core samples are not significantly different from the periods associated with the largest amplitude terms in the series expansion of the precessional parameters; the periods around 42000 yr are identical with the most important term in the expansion of the obliquity; and the peaks in the range of 106000 yr may be either a contribution from the eccentricity or a beat effect of precessional periods. Other periods that could be found in the geological record are identified.

Rat bile as a convenient source of secretory IgA and free secretory component

Abstract: Rat hepatic bile contains three proteins as major constituents: secretory IgA (SIgA), free secretory component (FSC) and albumin. Traces of alpha-macroglobulin, transferrin, IgG and IgM are also detectable. The bile duct daily pours between 5-12 mg each of SIgA and FSC into the rat duodenum. The origin and function of these proteins in bile may represent important clues in the understanding of the SIgA system.

Comparison of the Properties of Plasma Membrane-Bound and Mitochondria-Bound ATPases in the Yeast Schizosaccharomyces pombe

Abstract: 1 Two distinct membrane-bound ATPases of the glucose-grown yeast Schizosaccharomyces pombe are separated by differential and isopycnic gradient centrifugation. The mitochondrial ATPase, with optimal activity at pH 9.0, equilibrates with cytochrome c oxidase at densities 1.17 and 1.19 g × cm−3 while the non-mitochondrial ATPase, with optimal activity at pH 6.0 is associated with mannans in 1.21-g × cm−3 particles. Cytochemical staining for carbohydrates confirms the plasma membrane origin of vesicles found in a subcellular fraction enriched about 10 times in pH-6.0 ATPase activity. 2 The following analogies are found between the two purified membrane-bound ATPases. They hydrolyse preferentially ATP and require magnesium. They exhibit a Km of 3.3 mM for ATP-Mg at pH 6.0. The two activities are inhibited by ADP, Dio-9, dicyclohexylcarbodiimide, triethyltin, miconazole, sodium fluoride and p-hydroxymercuribenzoate. 3 Nevertheless, the plasma membrane-bound ATPase is distinct from the mitochondria-bound ATPase in the following properties. The plasma membrane-bound ATPase is not sensitive to the antibody dressed against the purified mitochondrial enzyme. Excess of Mg2+ inhibits the mitochondria-bound ATPase but not the plasma membrane one. The relative specificities for nucleoside triphosphates and cations of the two enzymes are different. In contrast to the mitochondrial enzyme, the plasma membrane-bound ATPase is not stimulated by carbonate and maleate anions. The plasma membrane-bound ATPase is not inhibited by the mitochondrial inhibitors oligomycin and venturicidin.

Circulating immune complexes in normal human pregnancy.

Abstract: CIRCULATING antigen–antibody (AgAb) complexes are important pathogenic factors in various diseases. In addition to their inflammatory effect, immune complexes can interfere with cellular immunity. For instance, in cancer, the so-called blocking factors are apparently circulating AgAb complexes1,2. Factors interfering with cellular immunity specifically directed against placental and foetal antigens have also been described in pregnancy serum3–5, and some data suggest a role of immune complexes as blocking factors in pregnancy6. We report here that circulating AgAb complexes are a constant feature of every normal pregnancy. This, of course, raises interesting questions as to the possible involvement of such complexes in the tolerance of the foetus by the mother.

Lot Sizing and Sequencing for N Products on One Facility

Abstract: The problem of determining both lot sizes and repeating sequences for N products on one facility is difficult due to the combinatorial and continuous nature of the problem. The work that has been done on the problem has made various assumptions “zero-switch rule” or “equal lot size,” for example to simplify the problem. Several heuristics have been suggested that come fairly close to a computable lower bound on cost. This paper discusses a mathematical programming formulation of the entire problem, along with reasons for its current nonpracticality. Heuristics for reducing the problem to a manageable mathematical programming formulation are presented. Specifically, a formulation is given when the sequence is known with both potentially unequal lot sizes and idle time periods as variables. The formulation is a convex quadratic program. Heuristics for finding sequences to feed to the quadratic program are explored, and examples from previous literature demonstrate that the methods here give consistent results as good as and sometimes significantly better than previous methods. Finally, we discuss situations in which such methods might be important and situations in which easier methods should suffice.

Binding sites related to ouabain-induced stimulation or inhibition of the sodium pump.

Abstract: THE concentration of free cardiac glycosides in the blood of patients treated for heart failure ranges between 1 and 5 nM (refs 1–3). Studies on human heart slices have shown that, within this range of concentrations, digitoxin does not inhibit the sodium pump but does stimulate 42K uptake3. Similar observations have been made with isolated guinea pig atria: low concentrations of ouabain (near 1 nM) stimulate 42K uptake whereas higher concentrations inhibit it4. These results are in agreement with recent electrophysiological observations on Purkinje fibres showing that low doses of ouabain produce changes in the K gradient that reflect stimulation of the sodium pump5. It has also been observed that the stimulation of the sodium pump by ouabain is associated with a positive ionotropic effect6. Earlier studies with guinea pig atria4 and other preparations7–9 showed that the binding of ouabain occurs on non-specific and specific sites. The specific binding is fitted by a Langmuir curve with an equilibrium constant close to that estimated by measuring the inhibition of the sodium pump. We report here the existence of a binding with a higher affinity associated with the stimulation of the sodium pump.

Long-term variations of the Earth's orbital elements

Abstract: Critical analysis of theories of the long-term variations of the ecliptical elements of the Earth leads to the following conclusions, regarding the influence of different terms on the accuracy of the expansions used: (a) further improvement in planetary masses will not have significant influence; (b) for the (/b e/, pi ) system, terms depending upon the second order as to the disturbing masses are more important than ones coming from the third degree with respect to the planetary eccentricities and inclinations; (c) for the (/b i/, Omega ) system the latter terms have highly significant influence, whereas additional terms in masses are negligible. The same conclusion can be drawn for ( epsiv , Psi /sub g/). Using these results, a new solution for the long-term variations of the Earth's orbital elements is obtained.

Microbiological aspects of spontaneous wort fermentation in the production of lambic and gueuze

Abstract: Lambic and Gueuze are special Belgian beers obtained by spontaneous fermentation. Micro-organisms involved in this fermentation were counted and differentiated using several selective growth media. Micro-organisms were also isolated from samples of Lambic of different age and originating from different casks and brews and identified by classical tests. The following general pattern of microbial development was observed. After 3 to 7 days the fermentation started with the development of wort Enterobacteriaceae and strains of Kloeckera apiculata. These organisms were overgrown after 3 to 4 weeks by strains of Saccharomyces cerevisiae and S. bayanus. These were responsible for the main fermentation, lasting for 3 to 4 months. This was followed by a strong bacterial activity. This period was dominated by the growth of strains of Pediococcus cerevisiae. These reached their maximal numbers during the summer months and were responsible for a fivefold increase in lactic acid concentration. In some casks they caused ropiness. After the main fermentation period Lambic is very sensitive to spoilage by acetic acid bacteria of the genus Acetomonas. The presence of air may be the determining factor for their development. After 8 months a new increase in yeast cells was noted. These belonged now mainly to the genus Brettano-myces bruxellensis and Br. lambicus. They caused a further slow decrease in residual extract and the appearance of special flavours. Oxidative yeasts of the genera Candida, Cryptococcus, Torulopsis and Pichia were also detected and may be responsible for the formation of a flim on the beer surface after the main fermentation.

Structural Analysis of the Transition Phases in the Kaolinite-Mullite Thermal Sequence

Abstract: Dehydroxylation phases of a kaolinite from Zettlitz, Czechoslovakia, were investigated by radial electron density distribution (RED) and X-ray spectroscopy. Special emphasis was placed on the 2 amorphous or poorly crystallized transition phases, i.e. metakaolinite (600 degrees to 800 degrees C) and the spinel structure (900 degrees C). The RED diffraction method, which is particularly suited to the study of such materials, indicated (1) a particularly expanded tetrahedral configuration for the Al atoms in metakaolinite and (2) a pure Al/sub 2/O/sub 3/ spinel structure. The first result confirms earlier observations; the second eliminates, for the experimental conditions and kaolinite studied, the possibility of the formation of an Al-Si spinel structure with the Al and Si occupying the octahedral and tetrahedral interstices, respectively. Complementary measurements on the Al/b K/ alpha line shifts for the same samples support the present interpretation. Determination of the apparent Si coordination number by the same spectroscopy procedure revealed a regular 4 coordination for all phases except the end-member mullite.

Genetics of ribosomal protein methylation in Escherichia coli. I. A mutant deficient in methylation of protein L11.

Abstract: Several thousand mutagenized clones of Escherichia coli were screened for methyl group incorporation into protein in crude extracts, in order to isolate mutants lacking the full complement of methyl groups in ribosomal proteins. One mutant isolated by this method and designated prm-1 incorporated 6–7 methyl groups per ribosome upon incubation of its ribosomes with a partially purified enzyme preparation from E. coli wild-type. The methyl groups were located exclusively in the 50S particle and for the most part (85%) in protein L11. Three methylated amino acids were detected: e-N-trimethyllysine, e-N-monomethyllysine, and an uncharacterized amino acid. These accounted respectively for 4.6, 1.3 and 0.9 methyl groups per ribosome. These results indicate that protein L11 in wild-type contains a stoichiometric amount of these methylated amino acids which are absent in mutant prm-1. Since this mutant is fully viable, its methylation deficiency does not result in a major defect in ribosome assembly or functioning.

The lansing effect revisited. ii.-cumulative and spontaneously reversible parental age effects on fecundity in drosophila melanogaster.

Abstract: Various lines of a wild strain of Drosophila melanogaster have been reproduced, generation after generation, at a young or an old age. Diverse traits related to fitness, and more specifically to life span and fecundity, have been measured almost at each generation in both kinds of lines. The cumulative and spontaneously reversible parental age effects-i.e. Lansing effectson life span have been described and discussed in the first paper of this series (Lints and Hoste, 1974). A hypothetical explanation for the Lansing effects, invoking modifications in molecular composition and configuration in relation to parental age was set forth. The purpose of the present paper is to see whether the data on fecundity, collected during the same experiment, do or do not support our hypothesis or otherwise shed light on the mechanism of Lansing effects as well as on the evolutionary theory of senescence.

Mitochondrial heredity of resistance to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of cytochrome b oxidation, in Saccharomyces cerevisiae.

Abstract: 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), an inhibitor of cytochrome b oxidation, has been used for the selection of three resistant mutants, (diur) of Saccharomyces cerevisiae. The mutant diur-64 exhibits in vivo cross-resistance to antimycin A while diur-34 and diur-1 are more sensitive to antimycin A than the parental strain. The three mutants exhibit mitochondrial inheritance according to the following criteria: mitotic segregation of diuron-resistant and diuron-sensitive diploids is obtained among the diploid progeny of a cross between diur and dius; non-Mendelian segregation of diuron resistance (4:0) is observed in spores of tetrads issued from diuron-resistant diploid; extensive ethidium bromide treatment leads to the formation of Q– mutants which no longer transmit diur and dius alleles. Evidence for two distinct diuron-resistant loci were obtained by allelism tests. Recombination analysis shows that diuron-resistance is not located in the polar region of the mitochondrial genome. The diur loci are not linked to the erythromycin locus since the upper limit in recombinants frequency (26%) for a non-polar region is obtained between diur and eryr. A low recombinants frequency (3%) is observed in crosses between diur-34 mutation and the two mutants cob1 and cob2 suggesting that diur-34 might be located between these two cytochrome-b-deficient loci. The resistance to diuron is also expressed in vitro since the oxidation rates of succinate by sonicated submitochondrial particles from the mutants are clearly less sensitive to diuron than that of the wild type.

Process for the removal of metals from solution

Abstract: Several metal ions, such as mercury, cadmium, copper, zinc, nickel and cobalt, may be removed from waste waters and similar solutions by treating such solutions with a cation exchanger in the presence of a polyamine. A treatment with clay minerals such as bentonite or montmorillonite in the presence of tetraethylenepentamine is preferred. The solution may be first combined with polyamine and then contacted with the cation exchanger, but in a preferred embodiment, the polyamine and cation exchanger are combined first to form a solid adsorbent and then contacted with the solution.

Hélicènes pontés: Ethano-3,15- et oxa-2-propano-3,15-[7]hélicène. Synthèse, spectrographie 1H-RMN. et étude par diffraction aux rayons X

Abstract: Bridged helicenes: 3,15‐ethano‐ and 3,15‐(2‐oxapropano)‐[7]helicene The title compounds (35 and 33, see Scheme 4) have been synthesized from a common intermediate: 3,15‐dimethoxycarbonyl‐[7]helicene (26). The conformation of the bridged [7]helicenes (X‐ray diffraction) and their 1H‐NMR. spectra have been compared to the conformation and 1H‐NMR. spectra of [7]helicene and 3,15‐dimethyl‐[7]helicene (10). Copyright © 1977 Verlag GmbH & Co. KGaA, Weinheim

On the uniqueness of the equilibrium state for plane rotators

Abstract: We study the classical statistical mechanics of the plane rotator, and show that there is a unique translation invariant equilibrium state in zero external field, if there is no spontaneous magnetization. Moreover, this state is then extremal in the equilibrium states. In particular there is a unique phase for the two dimensional rotator, and a unique phase for the three dimensional rotator above the critical temperature. It is also shown that there is a unique equilibrium state in a sufficiently large external field.

Reaction mechanisms of combustion in low pressure acetylene-oxygen flames

Abstract: In order to understand the fundamental mechanism of combustion processes, it is necessary to measure the concentrations of all the species throughout the flame front. Molecular beam sampling and mass spectrometric analysis have been used for that purpose. We have determined the molar concentrations of the stable and unstable species for two C2H2/O2 flames: a lean flame and a stoichiometric one. Both flames were burning at 40 Torr. From all these data, it is possible to deduce the elementary processes occurring in acetylene combustion. The first step of acetylene removal involves either hydroxyl radicals or oxygen atoms, in different proportions depending on the equivalence ratio: C2H2+O→CO+CH2(r.11)k11=6.7×1013 exp(−4000/RT)cm3mol−1s−1 C2H2+OH→C2H2O+H(r.8)k8=3.2×1011 exp(−200/RT)cm3mol−1s−1. The CH2 radical then reacts with molecular oxygen, producing carbon dioxide and molecular hydrogen. The ketene C2H2O reacts with a hydroxyl radical to form formaldehyde: C2H2O+OH→CH2O+CHO (r.7)k7=2.8×1013 cm3 mol−1 s−1, and CH2O further reacts with another hydroxyl radical: CH2O+OH→CHO+H2O Molecular oxygen then combines with the formyl radical CHO to give carbon monoxide: CHO+O2→CO+HO2 The CO and H2, formed in the combustion of acetylene, disappear through the usual elementary reactions.