Analysis of mechanism of formation of epidemic variant of disease activator

Pre-epidemic circulation of a multivariate agent is simulated. An assumption on the possibility of forming a new variant as a combination of properties of circulating variants is examined.     

Comparison of models of insulin release

A model for insulin secretion with a storage and a labile compartment, as well as a provisionary factor, is combined with a signal model in which the signal can be the difference between an excitation and an inhibition, or the difference in concentrations inside and outside some cell components. The model, using a single set of values for the parameters, accounts in a semiquantitative manner for all of the regularly appearing features of the insulin secretion from thein vitro perfused pancreas to a wide range of patterns of glucose and tolbutamide stimulation. Among the features which can be accounted for are: early and late secretion of insulin as a function of glucose in terms of a single parameter; the apparent depletion and recovery during a pulsed pattern of stimulation by tolbutamide; the hypersecretion following a short period of rest during a prolonged stimulation by glucose; the negative spike which occurs when the concentration of glucose, which has been maintained for a period of time, is suddenly reduced to a lower level; and the appropriate responses to slow and fast ramp functions of glucose concentration.     

Shapes of curves of pH-dependence of reactions

A simple case is considered in which the rate of a two-step reaction depends on pH because the intermediate formed in the first step has to gain (or lose) a proton before it can react in the second step, and in which the rate-determining step therefore changes with pH. The curves of reaction rate against pH are shown to be symmetrical, and the sharpest peak possible has a width at half its height of 1.53pH units, i.e. of 2log(3+2 radical2). Any particular curve for this situation proves to be identical with a curve that could be generated for the pH-dependence of a single-step reaction in which the rate is proportional to the concentration of a particular ionic form of a reactant. Curves for the latter situation, however, can have forms impossible for the former case in which the rate-determining step changes, but only if the protonations that activate and deactivate the reactant are co-operative. The peak can then become even sharper, and its width at half its height can fall to 1.14pH units, i.e. to 2log(2+ radical3).     

蓝尾石龙子精子的超微结构

蓝尾石龙子(Eumeces elegans)附睾以2．5％戊二醛和1％锇酸双重固定,按常规制作超薄切片,用H-600透射电镜研究观察精子的超微结构。精子由头部和尾组成,头部由顶体复合体和核组成,尾由颈段、中段、主段和末段组成。头部的顶体囊前部扁平,分为皮质和髓质,顶体下锥由类结晶状的顶体下物质组成,穿孔器顶端尖,、穿孔器基板塞子状,细胞核延长,核内小管缺,核伸展部前端具一电子透明区,核肩圆,核陷窝锥形。颈段具片层结构,近端中心粒和远端中心粒的长轴呈直角,9束外周致密纤维与远端中心粒相应的9束三联微管相联,向后与轴丝相应的9束双联微管相联,中央纤维与2个中央单微管相联。中段短,含有线状嵴的柱状线粒体,由连续的规则小卵状或小梯形致密体组成线粒体间的环状结构,纤维鞘伸入中段,终环紧贴于细胞膜的内表面。线粒体与环状结构的模式为：rs1／mi1,rs2／mi2,rs3／mi3,rs4／mi4,横切面上每圈线粒体数目为10个。主段前面部分具薄的细胞质颗粒区。纤维3和8至主段前端消失。轴丝复合体呈“9 2”型。蓝尾石龙子精子超微结构与已描述的石龙子科种类比较发现,与蜓蜥群和胎生群的石龙子相似;但没有发现石龙子科精子的独征。     

Simulations of action of DNA topoisomerases to investigate boundaries and shapes of spaces of knots

The configuration space available to randomly cyclized polymers is divided into subspaces accessible to individual knot types. A phantom chain utilized in numerical simulations of polymers can explore all subspaces, whereas a real closed chain forming a figure-of-eight knot, for example, is confined to a subspace corresponding to this knot type only. One can conceptually compare the assembly of configuration spaces of various knot types to a complex foam where individual cells delimit the configuration space available to a given knot type. Neighboring cells in the foam harbor knots that can be converted into each other by just one intersegmental passage. Such a segment-segment passage occurring at the level of knotted configurations corresponds to a passage through the interface between neighboring cells in the foamy knot space. Using a DNA topoisomerase-inspired simulation approach we characterize here the effective interface area between neighboring knot spaces as well as the surface-to-volume ratio of individual knot spaces. These results provide a reference system required for better understanding mechanisms of action of various DNA topoisomerases.     

Effects of the Timing of Flashes of Light during the Course of Cellular Rotation on Phototactic Orientation of Individual Cells of Cryptomonas

The swimming movement of Cryptomonas sp. cells generates a helical path, as a result of rotations with an average period of 500 milliseconds. When a flash of light at 570 nanometers for 20 microseconds was applied unidirectionally at intervals of 500 milliseconds, only a fixed side of each rotating cell was repeatedly exposed to the flashes of light. The relationship between the irradiated side of a cell and the phototactic orientation of the cell, rotating with a period of 475 to 525 milliseconds, was determined by infrared videomicrography. Only when the ventral sides of the cells were exposed to the flashes of light did their courses shift predominantly toward the light source. This result suggests that light is efficiently detected by the ventral side of these organisms.     

Measurement of invertase activity of cells of Saccharomyces cerevisiae

The determination of the invertase activity of intact yeast cells presents a critical point, that is, the blockage of the enzyme action at a given moment. In this paper seven blockage methods were compared: the addition of 0.010 M sodium hydroxide solution, addition of 0.010 M sodium carbonate solution, addition of 0.010 M sodium carbonate solution followed by centrifugation (9750g; 10 min), immersion of the reacting mixture in a boiling water bath, immersion of the mixture in a -15 degrees C bath, filtration through a Millipore membrane, and addition of the first Somogyi's reagent followed by immersion in a boiling water bath. Only the last two methods lead to a rapid and effective blockage of the invertase activity.     

Preparation and stereoconfigurations of heterodimers of pyrimidines

Using a novel C-alkylation procedure, four isomers of a heterodimer of a thymine-uracil derivative have been synthesized. With retention of configuration, the stereoconfigurations and the relative rates of alkylation at various sites can be assigned. This knowledge allows the unambiguous identification of the heterodimer isolated from the irradiation of a mixture of thymine and uracil in ice and from the acid hydrolysates of UV-irradiated DNA. By comparing the NMR data gathered from this set of a heterodimer with those sets of uracil and thymine homodimers, the effectiveness and the magnitude of a 1,2-shielding of a neighboring proton by a $\text{cis}$ CH₃-group of a cyclobutyl derivative may be suggested. In addition, taking advantage of the comparatively low solubility of the Ba-salt of this thymine-uracil heterodimer, its purification from an admixture of various photodimers was accomplished in a simple manner.     

Identification of images as a series of gradual transformations of geometrical figures

In the course of psychophysiological experiments with a tachistiscopic presentation of geometrical figures as transformations from a square into a triangle, the subjects worked out a distance scale for optical mouse movement depending on the degree of similarity between the presented figure and a square. This curve appears as a gradual decrease in the distance during the figure’s transformation from a square into a triangle. Significant variation in the shape of the curve was revealed upon exclusion of one of the images of the alphabet. The results are discussed in the context of the lateral inhibition phenomena and compared with the data of the theory of identification.     

Estimation of age and rate of increase of rare variants.

The problem considered is that of estimating the age or rate of increase of a variant on the basis of the present number of replicates observed in a population. In place of previous diffusion equation analyses of age probability distributions, the likelihood for the age is studied on the basis of a discrete branching process model. It is shown that variations inherent in the process of gene evolution in natural populations make it impossible to provide a reliable point estimate of the age of a specified variant, although the likelihood analysis provides a confidence interval which may place useful bounds on the period in which a variant originated. The observed distribution of numbers of several variants may also provide useful information. The problems of estimation are discussed with reference to rare variants arising in American Indian populations.     

Behavioural mode of action of deet: inhibition of lactic acid attraction

Using the mosquito Aedes aegypti in a novel olfactometer that measures movement towards and away from a stimulus, we could not confirm that 'deet' is a repellent of mosquitoes. In the absence of a host, deet was an attractant and in the presence of a host, it was an inhibitor of attraction. This inhibition occurred in the gaseous phase and was therefore not the result of the physical properties of deet. We determined that L-lactic acid, a component of human sweat that is an attractant to mosquitoes, is the target of this inhibition, implying that lactic acid may be a bottleneck in the behavioural cascade preceding blood-sucking.     

Structures of two repeats of spectrin suggest models of flexibility.

Spectrin is a vital component of the cytoskeleton, conferring flexibility on cells and providing a scaffold for a variety of proteins. It is composed of tandem, antiparallel coiled-coil repeats. We report four related crystal structures at 1.45 A, 2.0 A, 3.1 A, and 4.0 A resolution of two connected repeats of chicken brain alpha-spectrin. In all of the structures, the linker region between adjacent units is alpha-helical without breaks, kinks, or obvious boundaries. Two features observed in the structures are (1) conformational rearrangement in one repeat, resulting in movement of the position of a loop, and (2) varying degrees of bending at the linker region. These features form the basis of two different models of flexibility: a conformational rearrangement and a bending model. These models provide novel atomic details of spectrin flexibility.     

The patterns of elongation of the anterior part of the body of limbless squamata

The interpretation of original features of the aortic trunks showed by subterranean limbless Squamata allows to propose a hypothesis about a particular pattern of elongation regarding the anterior part of these Reptiles. The comparative morphological data supplies some arguments to the idea of the breaking of the topographical link between "scapular level - heart level" and the insertion of a new "precardiac" region which produces a backward displacement of the heart.     

Study of the kinetics of thermoinactivation of lysyl-tRNA-synthetase from the liver of x-irradiated rats

A study was made of the kinetics of thermoinactivation of lysyl-tRNA-synthetase isolated from rat liver at early times of radiation damage development after the effect of a minimum absolutely lethal X-radiation dose (0.21 C/kg). The thermostability of a dimer form of the enzyme was shown to be higher than that of a monomer. It was established that substrates had a stabilizing effect on the enzyme during thermoinactivation. On the basis of the data obtained from the studies in the kinetic properties of the enzyme and the thermoinactivation a conclusion is made that lysyl-tRNA-synthetase is stabilized during subunit aggregation. The thermostability of the enzyme was decreased by irradiation.     

An analysis of non-bonded energy of proteins

Non-bonded energy of 16 proteins was calculated using the atomic co-ordinates obtained by X-ray crystallography. The curve of total energy against the number of atoms in proteins is approximately linear with a slight concaved shape. According to a linear equation to fit the curve, the extrapolated length of a polypeptide chain of a globular shape is expected to be 18 residues, which corresponds conceivably to an approximate size of nucleus for a folding of the polypeptide chain. Contributions from short-range and medium-range energies are always much greater than those from long-range energy for all the proteins and there seems to exist a change of each contribution in a range from 1200 to 1700 atoms. The energies with a lag less than four residues are a major part of the total energy and the contribution of energy from main-chain atoms is considerably higher than that from side-chain atoms. Side-chain atoms of a residue have a tendency to interact more strongly with main-chain atoms of N-terminal, than with those of C-terminal side of the residue, indicating asymmetry of the interaction in a protein. Amino acid residues in proteins may be divided into three groups by the order of strength of average energy. The first group exhibiting strong interaction consists mainly of hydrophobic amino acids and the third group consists of hydrophilic ones corresponding to the location in a protein molecule. Cys, val, leu and met are important for medium-range and long-range energies; gly and ala for medium-range energy; ile, trp, phe, tyr and arg for long-range energy. One simple application of the average energy of amino acid residues is illustrated to estimate local energy of a segment of nine residues given by a protein sequence. There is a good correlation between the curve computed by the average energy and the experimental curve for myoglobin.     

Comparative kinetics of appearance in the portal vein of alpha-aminated nitrogen from mixtures of small peptides of free amino acids of the same composition introduced in the duodenum of conscious pigs

The quantitative kinetics of appearance of amino acids (a.a.) in the pig portal vein was studied in 6 animals for 5 hrs. after duodenal perfusion of an enzymatic hydrolysate of milk proteins or a solution of free a.a. of the same composition. Each product was given in two quantities (55 and 110 g). The quantities of a.a. appearing in the portal vein were higher after perfusion of the hydrolysate than after that of the free a.a., independently of the time after the perfusion. Thus, nitrogen present in the small intestine as small peptides is absorbed more quickly than when it is present as free amino acids.     

Location of the Origin of Transfer of the Sex Factor F

The location of the origin of transfer on the map of Flac has been determined by two different techniques. The first showed that no transfer cistrons were transferred early by a transposition Hfr strain with a known point of chromosomal integration into Flac, and the second used a series of transfer-deficient Hfr deletion strains to map a locus required in cis for chromosome transfer by an incoming Flac factor. Both techniques gave results consistent with a location for the origin of transfer between traJ and the phi(R) (11) locus.     

Pathogenicity of two species of Fusarium on some cultivars of bean in greenhouse

Twenty isolates of Fusarium oxysporum and F. solani were isolated from the infected roots of bean in different farms of east Azarbaijan and Tehran Provinces and their pathogenicity determined. Most isolates of the fungi were identified as F. oxysporun. They caused root rot, yellowing and wilting of bean in the field. In this test, the roots of 6 cultivars of bean seedlings soaked in suspension of the 7 isolates of the fungi (a1, Gogan, a2, Bilverdi, a3, Savojbolagh-Hashtgerd, a4, field of Agr. Coll. a5, Khomein, a6, Ramjin of F. oxysporum and a7 of F. solani of Varamin, Iran) for 5 minute (106 spores/ml.) then transplanted into the sterilized soil in 4 pots (as replication). For control (a8) the roots soaked in distilled water. The results showed that percentage average of necrotic roots and crowns of isolates al, a2, a3, a5, a6, a7 was %20.31 in group a, a4 was %43.52 in group b and a8 was %2.77 in group c after 3 weeks. The isolate a4 (from the field of Agricultural College, Karaj) was more infectious than the other because it caused wilting, yellowing the leaves and decreased the growth very soon, followed by a5 with %25.32 rate was more pathogenic. Bean cultivar Goli-Red was more tolerant with %10.02 than the others of 16.29 (Naz Red) to 25.15 percent of necrotic the roots & stems.