Organisation de la phase minérale chez Vaceletia crypta (Vacelet)Démosponge,Sphinctozoaire actuelle. Comparaison avec des formes aragonitiques du Trias de Turquie

The fundamental microstructural and ultrastructuralcaracteristics of a non fibrous carbonate tissue has been revealed by the study of the only living Sphinctozoa: Vaceletia crypta (Vacelet), Demospongia.These observations yield important data for interpretation of homogeneous carbonate structure in the skeleton of some fossil sponges. Effectively, we notice that two triassic forms, morphologically very different (Sphinctozoa and Inozoa) show remarkable microstructural analogies with Vaceletia crypta. These considerations should not be leaved out to establish an only classification of Sponges, joining both living and fossil forms.Moreover, the elementary skeletal constituants ofthe two forms show dimensions which indicate a growth in size in comparison with the living species. This increase has probably a diagenetic origin (adjunction of aragonite). So it appears that the present aspect of the mineral components cannot result from a reduction in size (micritization), as has been sometimes asserted.     

THE ROLE OF GLUCOCORTICOID HORMONES IN THE CONTROL OF EPIDERMAL MITOSIS

It has previously been established that the epidermal chalone inhibits epidermal mitotic activity more powerfully in the presence of adrenalin, although adrenalin itself is not a mitotic inhibitor. It is now shown that in low concentrations hydrocortisone has little if any antimitotic activity, that when it is present together with chalone and adrenalin it does not markedly increase their antimitotic activity, but that it does act to prolong the mitotic depression which they induce. It is known that, without hydrocortisone, adrenalin rapidly escapes from epidermal cells so that the chalone action is weakened. It appears that the role of hydrocortisone may be to reduce the rate of adrenalin loss and thus to prolong the chalone-adrenalin activity. It is also shown that the rate of loss of adrenalin from epidermal cells is inhibited, though to a much lesser extent, in the presence of excess chalone.     

THE ROLE OF STRESS HORMONES IN THE CONTROL OF GRANULOCYTE PRODUCTION

It has previously been indicated that the inhibitory power of the granulocytic chalone is not influenced by adrenalin. It is now shown that this is true both in absence and in presence of exogenous hydrocortisone. It is also shown that hydrocortisone itself does not cause significant inhibition of DNA synthesis in rat bone marrow cells in vitro, but that it does act to augment the inhibitory effect which the granulocytic chalone induces. It is suggested that the primary action of hydrocortisone may be on the cell membrane which changes the cell wall permeability to chalone, perhaps by reducing its rate of loss from the cells.     

Statistical distributions of root maximum growth pressures,root buckling stresses,and soil penetration strengths

Summary It is shown that root maximum growth pressures, root buckling stresses, and soil penetration strengths and all non-normally distributed with positive skew. It is found that a Beta distribution, with assigned end points, provides an extremely good fit in each case. It is recommended that this Beta distribution is used in the development of mathematical models for root growth in soil.     

Purification and properties of a ribonuclease in human urine that hydrolyses polycytidylic acid.

Human urine RNase was purified about 2000-fold. The preparation is free from phosphatase, phosphodiesterase and DNase activities. On electrophoresis through polyacrylamide gel at pH 8.3, it migrates toward the anode and stains with periodic acid-Schiff reagent, suggesting that it is acidic and glycoprotein in nature. Its isoelectric point is at pH 4.1. It has a molecular weight of about 21,500. It is thermostable at pH 4.2 and thermolabile at pH 8.5. It has a pH optimum at 6.5. It exhibits highest preference for cytidine 3'-phosphate linkages. Its activity on poly (C) is endonucleolytic. It cleaves poly (C) via intramolecular transphosphorylation. It has no action on cytidine 2': 3'-cyclic phosphate or uridine 2':3'-cyclic phosphate. Its rate of hydrolysis of poly (U) is less than 2% of that of poly C). Poly (A) and poly (G) are totally inert to its action. Its action on poly (C) is inhibited by poly (G), poly (A) and poly (U). It differs from bovine pancreatic Rnase A in its physical, chemical and catalytic properties. It is, however, similar to human serum and pancreatic RNase in all its properties, suggesting that pancreas is its likely source.     

Meiofauna and the origins of the Metazoa*

Possible alternative habitats and life-styles of the original metazoan are considered. It is argued from the dominance of the benthic habitat in present-day groups that the original metazoan habitat was benthic rather than planktonic. Similarly, plesiomorphic metazoan taxa tend to be holobenthic rather than pelago-benthic. It is therefore probable that the early Metazoa were holobenthic. The concept of plesiohabitats and apohabitats in the evolution of taxa is presented. This leads to the proposition that the early metazoans were interstitial bionts of fine sand. Finally, the controversy concerning the aerobic or anaerobic origin of the Metazoa is considered. It is shown that competition theory predicts that plesiomorphic taxa are likely to remain in plesiohabitats. Diagrams showing the possible evolution of major taxa in relation to available habitats are presented. It is concluded that the earliest Metazoa could have evolved in anaerobic marine sand and that the early Plathelminthomorpha and Aschelminthes did so.     

Metabolic regulation of neuron functions

A short analytical review of Soviet and foreign studies devoted to metabolic regulation of neuron functioning is presented. It is shown that the electrical activity of neuron is accompanied by structural changes and an increase in RNA content. It is assumed that these changes are initiated by calcium ions, coming to the neuron during its excitation. The principles of metabolic regulation of functioning of electro- and chemoexcitable neuronal membranes are considered. It is shown that the metabolic reactions can be an intermediate between the activated chemoreceptor and the electrical response of the cell. Evidence is presented that the electroexcitable and chemosensitive structures in the membrane modulate each other. The role of intracellular messengers in regulating the activity of receptors and channels is considered. Possible mechanisms for their modifications under the influence of cellular factors are discussed. It is shown that the work of neuron is controlled by several metabolic regulatory systems simultaneously.     

Nature and possible origin of Human Serum ribonuclease

Human Serum contains an acidic RNase which is glycoprotein in nature. It is thermostable at pH 4.2 and thermolabile at pH 8.5. It has a pH optimum at 6.5. Its activity either on poly (C) or RNA is endonucleolytic and is absolutely dependent on citrate or phosphate. It exhibits highest preference for the secondary phosphate esters of cytidine 3′-phosphates. It has no action on cytidine 2′:3′-cyclic phosphate. Poly (A) and poly (G) are not only refractory to its action, but also inhibit its action on poly (C). Its rate of hydrolysis of Poly (U) is about 2% of that of poly (C). It differs from bovine pancreatic RNase. It is, however, similar to human pancreatic RNase suggesting that its primary source is pancreas.     

Some remarks about plasma mechanical resistance

It is notoriously difficult to assess inflammatory activity in clinical practice and the profusion of proposed assessment methods bespeaks the inadequacy of each. It was these problems with classical methods that led the authors to the study of plasma mechanical resistance (a quantity related to viscosity). They describe the apparatus and the technical procedure, that is more germane to normal clinical practice. It is hoped that further studies will confirm author's findings.     

Backward bifurcation of an epidemic model with treatment

An epidemic model with a limited resource for treatment is proposed to understand the effect of the capacity for treatment. It is assumed that treatment rate is proportional to the number of infectives below the capacity and is a constant when the number of infectives is greater than the capacity. It is found that a backward bifurcation occurs if the capacity is small. It is also found that there exist bistable endemic equilibria if the capacity is low.     

Purification and Properties of a Ribonuclease in Human Urine that Hydrolyses Polycytidylic Acid

Human urine RNase was purified about 2000-fold. The preparation is free from phosphatase, phosphodiesterase and DNase activities. On electrophoresis through polyacrylaraide gel at pH 8.3, it migrates toward the anode and stains with periodic acid-Schiff reagent, suggesting that it is aci c and glycoprotein in nature. Its isoelectric point is at pH 4.1. It has a molecular weight of about 21, 500.

It is thermostable at pH 4.2 and thermolabile at pH 8.5. It has a pH optimum at 6.5. It exhibits highest preference for cytidine 3′-phosphate linkages. Its activity on poly (C) is endonucleolytic. It cleaves poly (C) via intramolecular transphosphorylation. It has no action on cytidine 2′: 3′-cyclic phosphate or uridine 2′:3′-cyclic phosphate.

Its rate of hydrolysis of poly (U) is less than 2% of that of poly (C). Poly (A) and poly (G) are totally inert to its action. Its action on poly (C) is inhibited by poly (G), poly (A) and poly (U).

It differs from bovine pancreatic RNase A in its physical, chemical and catalytic properties. It is, however, similar to human serum and pancreatic RNase in all its properties, suggesting that pancreas is its likely source.     

Cooperative bimetallic reactivity

A number of bimetallic complexes of a macrocyclic binucleating ligand containing both six- and four-coordinate binding sites have been prepared in order to try to reproduce the behavior of certain metalloproteins. It was found that two-metal oxidation is severely impeded in bimetallic systems. It is postulated that the mutual deactivation of metal oxidation is principally the result of unfavorable ligand conformational adjustments which occur after the first metal is oxidized. It is shown that when these conformational restraints are removed, two-metal oxidations are possible.     

Membrane action of ionic surfactants on yeast cells]

Effect of a number of homologous series of cationic and anionic surfactants on yeast cells was examined. It is found that the cellular proteins extraction degree under the surfactants treatment depends on the agents structure. It is established that the highest extraction efficiency among the bisquaternary ammonium compounds is displayed by the decyl derivatives and among sodium alkyl sulfates--by octyl sulfate. The influence of pH, ionic strength and the agent concentration on the proteins extraction degree was studied. It is concluded that the anionic and cationic compounds act on the yeast plasma membrane by the similar way and all the differences observed are just the quantitative ones. It is suggested that the efficiency of the surfactant action on the cell is limited particularly by the ratio of cell wall pore size to the size of micelles formed by the agent in the solution.     

Membrane mechanisms of testosterone action]

The experiments on adult Wistar rats have shown that testosterone administration provoke hyperpolarization of hepatocytes and adrenocorticocytes plasmatic membranes. It was discovered that this hyperpolarization was caused by cell Na, K-ATPase activation. Inhibitors of protein biosynthesis prevent both testosterone-induced hyperpolarization and Na, K-ATPase activation. It is shown that some hyperpolarization factor appeared in the cytosol and blood serum under testosterone influence. It was suggested that this mechanism is mediated by cell genome.     

Meiosis readiness in Lilium

It was observed in five cultivars and two hybrids of Lilium that premeiotic prophase is retarded in anthers approaching meiosis. The occurrence of premeiotic despiralization was related to the degree of retardation of premeiotic prophase. It is proposed that meiosis is initiated by stimuli arising outside the premeiotic cells. It is suggested that an accumulation of meiosis-inducing substances in the cytoplasm of the premeiotic cells causes prophase to slow down; when a critical level ("meiosis readiness") is reached, mitotic division is no longer possible and cells in premeiotic prophase despiralize to interphase.     

Effects of dispersal on the stability of a prey-predator system with functional response

Using Liapunov's direct method, effects of dispersal on the linear and nonlinear stability of the equilibrium state for a prey-predator system with functional response are investigated. It is noted that the functional response has a destabilizing effect. It is shown that an otherwise linearly or nonlinearly stable equilibrium state of the system remains so with dispersal as well, even with functional response. It is further established that if the equilibrium state is linearly stable a subregion of the positive quadrant can be found in the phase plane where it is nonlinearly stable with or without dispersal.     

A Structure-Activity Relationship for the Hydrolysis of Acetylamino Acids by Porcine Aminoacylase

A structure-activity relationship is presented that satisfactorily predicts the rates of hydrolysis of a series of acetylglycine derivatives by porcine aminoacylase. It is apparent that the substrate specificity of aminoacylase is mainly kinetic in origin, the observed correlation with Taft's E(s) parameter supporting the notion that enzymolysis proceeds through a mechanism that is analogous to chemical hydrolysis. It is suggested that the alpha-CH(2)CH group of those substrates that possess this moiety is conformationally immobile upon binding. This lock facilitates rapid hydrolysis and results from steric interactions between the enzyme and substrate. The incorporation of alpha-methyl amino acid derivatives in the structure-activity relationship is consistent with a flexible active site model and it is concluded that the alpha-methyl effect in this system is a binding phenomenon. It is evident that the active center of porcine aminoacylase can comfortably accommodate amino acid derivatives with side chains containing less than six carbon atoms, contrary to previous assertions. It is suggested that the binding of bulkier derivatives necessitates the distortion of the active site. Derivatives possessing beta-hydroxyl groups are found to deviate from expected behavior and a nonproductive binding model is presented. Copyright 2000 Academic Press.     

Energizing plasmalemma of yeasts is necessary for activation of its H+-ATPase by glucose]

ATPase of yeast plasmalemma is known to be activated during incubation of cells or protoplasts with glucose. It has been shown that the level of ATPase activation is sharply decreased after pretreatment of cells or protoplasts with mercaptoethanol, dinitrophenol, gramicidin D, nigericin, or monensin. It is suggested that deenergization of yeast plasmalemma by monensin, nigericin, and mercaptoethanol as uncoupler plays a crucial role in the prevention of in vivo activation of plasma membrane ATPase by glucose. It is concluded that energization of yeast plasmalemma is necessary for activation of ATPase by glucose.     

作物水分代谢及其调节

简要评述了作物水分吸收、散失过程及其影响因素,对气孔的调节机制、量化控制研究现状进行了分析。对根系水分倒流、气孔最优化调节、气孔不均匀关闭进行了介绍。     

A new endoribonuclease from Escherichia coli. Ribonuclease N.

A new ribonuclease called RNase N was isolated from Escherichia coli. It is a nonspecific endoribonuclease that can cleave rRNA, poly(U), and poly(C) to small oligonucleotides and 5'-mononucleotides. It requires monovalent cations and is inhibited by divalent cations. It is suggested that this enzyme plays a role in the decay of rRNA,under various starvation conditions and perhaps in the decay of mRNA.