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1.
T.W. Barrett 《Journal of theoretical biology》1982,99(2):293-307
In Part I (Barrett, 1981), the concept of chemical parametric excitation was reviewed and applied to the process of nerve action potential excitation and regeneration. In the present paper, the chemical reactions involved in muscle contraction and the enzymatic reaction are examined and shown to be examples of chemical parametric excitation.It is demonstrated that in a model biochemical scheme for an enzymatic reaction, the enzyme is activated from a state, X, to a state, , and in this activated state pumps the reaction parametrically. The concept of enzyme is identified with an excited state or state of disequilibrium permitting a release of energy during the dissipation, , in the enzymatic reaction, which is powered by the release of energy in the return to the unexcited state X. The demonstration of parametric excitation relations for chemical systems indicates an explanation for the directionality of energy flow and designates an energy pumping role for an enzyme.In muscle contraction, the role of is played by actomyosin and Ca2+, and the enzymatic reaction is the hydrolysis of ATP. The release of energy caused by this hydrolysis reaction brings about the conformational changes underlying muscle contraction. 相似文献
2.
3.
《Mathematical biosciences》1987,87(2):173-198
This paper primarily expounds upon the problem of persistent age-state distribution functions for the dispersion of structured populations. A general model is introduced, based on the following assumptions: 1) the state of an individual of age a is characterized by a set of random variables X1, X2,…, XQ (weight, size, etc.) obeying a phenomenological master equation; 2) the birth function λ depends on the age a' of parents and on the state variables X1,…, XQ of the newborns; 3) the mortality function is composed of two additive terms—the first contribution depends only on age while the second contribution depends on the total population density; 4) the population diffuses to avoid crowding. These hypotheses define a nonlinear population model for which time- and space-persistent age-state distribution functions eventually may occur even if the total population density is time- and space-dependent. A biological interpretation of the main results is given in terms of the distribution function of the state vector at birth. In the last part of the paper a generalized model is presented, assuming that the behavior of an individual is described by a system of age-dependent master equations [29]. 相似文献
4.
This work is concerned with the growth of age-structured populations whose vital rates vary stochastically in time and with the provision of confidence intervals. In this paper a model Yt + 1(ω) = Xt + 1(ω)Yt(ω) is considered, where Yt is the (column) vector of the numbers of individuals in each age class at time t, X is a matrix of vital rates, and ω refers to a particular realization of the process that produces the vital rates. It is assumed that {Xi} is a stationary sequence of random matrices with nonnegative elements and that there is an integer n0 such that any product Xj + n0 ··· Xj + 1Xj has all its elements positive with probability one. Then, under mild additional conditions, strong laws of large numbers and central limit results are obtained for the logarithms of the components of Yt. Large-sample estimators of the parameters in these limit results are derived. From these, confidence intervals on population growth and growth rates can be constructed. Various finite-sample estimators are studied numerically. The estimators are then used to study the growth of the striped bass population breeding in the Potomac River of the eastern United States. 相似文献
5.
Yoshiyuki Asai Masanobu Uemura Masao Matsumoto Hitoshi Kanamori 《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2010,26(4):209-215
This paper proposes a new technique for reducing the patient dose when employing medical radiographs prepared by using screen-film systems. In this technique the patient dose can be reduced by employing scattered X-rays in order to obtain the same film density as that realized without the use of scattered X-rays. The minimum perceptible thickness difference ΔXmin, which can be recognized by liminal vision, was psychophysically calculated by considering the energy spectrum of incident X-ray, sensitivity spectrum of the screen layer, and the perception capability of human vision. From the calculated ΔXmins in various conditions, the permissible upper limit of scatter fraction for obtaining the same ΔXmin for three kinds of luminances, and the fraction of reduction in the primary X-rays were determined.As an example of the results, when the object size required for perception is 1.3 mm, a scatter fraction up to 42% can be permitted at a density D of 1.0 for a luminance of 2548 cd m?2. When we increase the luminance of the viewer from 478 cd m?2 to 2548 cd m?2, the upper limit of the permitted scatter fraction varies from 30% to 42% at a D of 1.0, i.e., the patient dose can be reduced by 17% under the same perceptibility of ΔXmin by utilizing scattered X-rays. This reduction can be successfully achieved by changing the lead content of the grid from 0.45 to 0.38 g cm?2. 相似文献
6.
The phylogenetical relationship of the fleas (Aphaniptera=Siphonaptera) to the other orders of the Insecta remains unsolved. Comparative studies of the cytology of the fleas are undertaken in an attempt to elucidate this problem. Two populations of Xenopsylla cheopis Rothschild, 1903, exhibit a chromosome complement of 2n = 14 A + X1X2Y (male): 14 A+X1X1X2X2 (female). The X1X2Y-sex-trivalent is restricted to the male meiosis, in oogenesis two sex-bivalents (X1X1 and X2X2) are formed. One population of Leptopsylla segnis Schönherr, 1811 shows 2n =18 A + XY (male): 18 A+XX (female). The high chromosome number of X. cheopis, L. segnis, and N. fasciatus (Bayreuther, 1969), the diffuse premeiotic stage in the spermatogenesis of the threespecies investigated and the multiple sex-chromosome-mechanisms of X. cheopis and N. fasciatus do not support the concept of a closer phylogenetic relationship between the Aphaniptera and Nematocera, but do not preclude the possibility of a kinship of Aphaniptera and Neomecoptera. Additional studies of the cytogenetics of these two orders are required before lasting conclusions can be drawn. The analysis of the chromosome cytology of the fleas of the Marsupialia, which are considered to be the most primitive of all living forms, could prove particularly instructive. 相似文献
7.
Steps by which a nonliving chemical system could have transformed into a living system are described and discussed, assuming general features of Wächtershäuser's chemo-autotrophic surface theory of the origin of life. Environmental species such as CO2 and H2S are proposed to have reacted to form a quasi-steady state metal-bound intermediate (CH3-M) that slowly decayed into waste (CH4). Unpredictable dispersive reactions expanded the system to include surface-bound forms of the citric acid cycle intermediates (oxaloacetate → citrate). Further reaction yielded an autocatalytic system in which raw materials are converted into the system at exponential rates. Combinatorial dispersive reactions that improved the performance of this system were automatically selected and incorporated into it. Systems evolved critical features of living systems (proteins, membranes, proteins, nucleic acids, etc.) using two related mechanisms called grafting and waste-conversion. Such living systems were transformed from less recognizable types (characterized by autocatalytic spreading, decentralization, poorly defined boundaries, etc.) into more recognizable ones (encapsulated by membranes, controlled by single-molecule genomes, etc.) that self-replicated by a cell division cycle and could evolve by the standard gene-based Darwinian mechanism. The resulting systems are viewed as having an autocatalytic network composed of three linked autocatalytic subreactions. 相似文献
8.
The anion–π interactions between Br? , Cl? , F? and H? anions and hexafluorobenzene (HFB), 1,2,4,5-tetracyanobenzene (TCB) and tetracyanopyrazine (TCP) have been studied by standard and counterpoise (CP) corrected methods at HF, B3LYP and MP2/6-31+ + G (d,p) levels of theory. The complexation energies were corrected for basis set superposition error (ΔE BSSE) and zero point energy (ΔE BSSE + ZPE). Also, the B3LYP results were corrected by single-point calculation at B3LYP/aug-cc-PVTZ level of theory. Although the CP-corrected method results in higher distances between anions and rings, the standard method gives lower complexation energies. TCP…X? series gives higher complexation energies in both CP-corrected and standard methods. Topological analysis of the charge density ρ(r) has been performed by the means of atoms in molecules method on the wave functions obtained at MP2/6-31+ + G (d,p) level of theory. The number and the nature of critical points depend on aromatic ring and anion. Natural bond orbital analysis indicates that nX → π*CC and nX → π*CN interactions are the most important interactions for TCB (and HFB)…X? and TCP…X? complexes, respectively. 相似文献
9.
The 2-monoacylglycerol acyltransferase (EC 2.3.1.22, acylglycerol palmitoyl transferase) catalyzes the synthesis of X-1,2-diacylglycerols from 2-monoacylglycerol and acyl CoA with an apparently variable stereochemical specificity. A microassay for determining the ratio of sn-1,2- and sn-2,3-diacylglycerols formed by the acylation of radioactive 2-monoacylglycerol in intact cells or in cell-free systems in the presence of free fatty acids and cofactors has been developed. The diacylglycerols are isolated by thin-layer chromatography using nonradioactive racemic diacylglycerols as carriers. The enantiomer content is determined following a chemical synthesis of X-1,2-diacylphosphatidylcholines and a stereospecific stepwise release of the sn-1,2- and sn-2,3-diacylglycerols by phospholipase C. By using thin-layer chromatography for the isolation of the hydrolysis products, known samples ranging in enantiomer ratios from 0.05 to 20 and containing 5000 to 200,000 cpm can be assayed to within 1% of the major and within 10% of the minor enatiomer content. The method is applicable to the determination of the enantiomer content of X-1,2-diacylglycerols generated via other acyltransferases and via lipolysis of triacylglycerols and diacylglycerolphospholipids in other biological systems. 相似文献
10.
The effect of modifying calcium concentration on the expression of the photosynthesis circadian rhythm was examined in Euglena gracilis, Klebs strain Z. Expression of the oxygen evolution rhythm required the presence of both extracellular and intracellular calcium. Several treatments were found to uncouple the rate of the light reactions from the biological clock. In the presence of these chemical agents, the rate of oxygen evolution increased steadily throughout the light portion of the light/dark cycle, instead of showing a peak of activity in the middle of the light cycle. Oxygen evolution was uncoupled from the biological clock when extracellular calcium concentrations were altered by the presence of EGTA or LaCl3. Uncoupling was also observed when intracellular calcium concentrations were disrupted by the use of Ca2+ channel blockers, the intracellular Ca2+ antagonist 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate, or by disrupting expression of the inositol trisphosphate system. Uncoupling was also observed when the diacylglycerol signaling system, which activates kinase C, was inhibited by acridine orange. The inhibition was reversed by the presence of phorbol esters which activate the kinase. It was concluded that both the inositol trisphosphate and diacylglycerol signaling systems were required for the expression of the oxygen evolution rhythm generated by the biological clock. 相似文献
11.
Min Ma Shi Chen Bao-yan Zhu Bai-Wei Zhao Hua-She Wang Jun Xiang Xiao-Bin Wu Yi-Jia Lin Zhi-Wei Zhou Jun-Sheng Peng Ying-Bo Chen 《PloS one》2015,10(1)
Aims
To assess the clinical significance and risk factors of solitary lymph node metastasis (SLM) in gastric carcinoma and establish a more accurate method to evaluate the possibility of lymph node metastasis (LM).Methods
A total of 385 patients with gastric carcinoma who underwent D2 lymphadenectomy at the Cancer Center of Sun Yat-Sen University were included in this research. Then we used a group of data from Sun Yat-sen University Gastrointestinal Hospital (SYSUGIH) to validate the accuracy of our developed method. The χ2 test, Kaplan–Meier analysis, log-rank test, COX model, and discriminate analysis were used to analyze the data with SPSS13.0.Results
We found that the LM number and pathological T staging were independent prognostic risk factors. CEA grading, LN status by CT, and T staging by CT were independent risk factors for LM in gastric carcinoma. In addition, we developed the equation Y = -5.0 + X 1 + 1.8X 3 + 0.7X 4 (X 1 = CEA grading, X 3 = LN status by CT, X 4 = T staging by CT) to evaluate the situation of LM. The data from SYSUGIH shows this equation has a better accuracy compared with CT.Conclusions
SLM is an independent risk factor in gastric cancer. And there was no survival difference between the skip metastasis group and the other SLM group (P = 0.659). It is inappropriate for the patient with SLM doing a standard D2 lymphadenectomy, due to the fact that LM rarely occurs in the splenic artery, splenic hilum. The risk factors for LM include CEA grading, LN status by CT, and T staging by CT. And we can use Y = -5.0 + X 1 + 1.8X 3 + 0.7X 4 (X 1, CEA grading, X 3 = LN status by CT, X 4 = T staging by CT, the critical value is 0.3) to estimate the possibility of LM, which has a better accuracy compared with CT. 相似文献12.
B. F. J. Manly 《Biometrical journal. Biometrische Zeitschrift》1981,23(3):267-281
The situation is considered where the multivariate distribution of certain variables X1, X2, …, Xp is changing with time in a population because natural selection related to the X's is taking place. It is assumed that random samples taken from the population at times t1, t2, …, ts are available and it is desirable to estimate the fitness function wt(x1, x2,…,xp) which shows how the number of individuals with Xi = xi, i = 1, 2, …, p at time t is related to the number of individuals with the same X values at time zero. Tests for population changes are discussed and indices of the selection on the population dispersion and the population mean are proposed. The situation with a multivariate normal distribution is considered as a special case. A maximum likelihood method that can be applied with any form of population distribution is proposed for estimating wt. The methods discussed in the paper are illustrated with data on four dimensions of male Egyptian skulls covering a time span from about 4500 B.C. to about 300 A.D. In this case there seems to have been very little selection on the population dispersion but considerable selection on means. 相似文献
13.
Distinguishing things from beings, or matters from lives, is a fundamental question. Extending E. Schr?dinger's neg-entropy and I. Prigogine's dissipative structure, we propose a chemical kinetic view that the earliest "live" process is embedded essentially in a special interaction between a pair of specific components under a particular, corresponding environmental conditions. The interaction exists as an inter-molecular-force-bond complex(IMFBC) that couples two separate chemical processes: one is the spontaneous formation of the IMFBC driven by a decrease of Gibbs free energy as a dissipative process; while the other is the disassembly of the IMFBC driven thermodynamically by free energy input from the environment. The two chemical processes coupled by the IMFBC originated independently and were considered non-living on Earth, but the IMFBC coupling of the two can be considered as the earliest form of metabolism: the first landmark on the path from things to a being. The dynamic formation and disassembly of the IMFBC, as a composite individual, follows a principle designated as "… structure for energy for structure for energy…", the cycle continues; and for short it will be referred to as "structure for energy cycle". With additional features derived from this starting point, the IMFBC-centered "live" process spontaneously evolved into more complex living organisms with the characteristics currently known. 相似文献
14.
John Z. Hearon 《Bulletin of mathematical biology》1965,27(1):291-303
An arbitrary set of chemical reactions is considered to occur among chemical speciesX
i
. In a closed uniform reaction system certain linear combinations of the concentrations of theX
i
are constants. The general construction of all such linear combinations with non-negative coefficients is given in terms of
the molecular formulae for theX
i
. It is shown that to each such linear combination there corresponds another which is a harmonic function when the reactions
take place in an open spatially distributed stationary reaction system of arbitrary shape. Under the usual boundary conditions
these harmonic functions are constants. With some restrictions upon the diffusion and permeability coefficients these constants
are evaluated. This evaluation is the basis for relations between the total concentration of a given chemical group (e.g.,
the sum of the concentrations of a free molecule, or ion, and its various bound forms) in the reaction system, and in the
surrounding medium. The bearing of these relations on apparent active transport is noted and illustrated. 相似文献
15.
The rate constants of ion-molecule reactions which are of potential significance in astrochemical systems are found to exhibit significant, and in many cases, negative temperature dependences. The rate constants of fast ion-polar molecule reactions (e.g., XH++B»BH++X) may increase by a factor of 5–10 between 1000 and 10K. Slow reactions that proceed via reaction complexes (e.g., H-transfer and association reactions) often exhibit temperature dependences of the formk=AT −n ,n=1–5. Both transition state theory considerations and the coupled-oscillator RRK-type model are seen to be able to account qualitatively for the behavior of slow ion-molecule, reactions. 相似文献
16.
T.W. Barrett 《Journal of theoretical biology》1981,92(3):185-207
In previous papers (Barrett, 1977b, 1980), the concept of chemical paramemetric excitation was applied to a number of diverse chemical phenomena and contrasted with the concept of chemical resonance, which is a special case of parametric excitation. In the present paper, its status as the fundamental concept of energy transfer and molecular switching is indicated, providing a mechanically sound explanation of nerve excitation at a basic level.The mechanism addressed by the parametric excitation concept is intermediate between macroscopic models of membrane assymetry and molecular models. No assumptions are made concerning the related macroscopic processes, but a systematic approach to organizational aspects of the processes involved in energy transfer is proposed.The chemical analog of the Manley-Rowe relations, which are the power conservation relations for parametrically excited electrical networks, is also derived. The demonstration of such Manley-Rowe relations for chemical systems indicates, for the first time, an explanation for the directionality of flow of power, and thus designates a pumping role. The generalized Manley-Rowe relations translated into flow, reaction, as well as oscillatory system terms, are suggested to be a universal law. Non-linearity is due to the coupling of three systems—each separately describable by Onsager linear relations—by the generalized Manley-Rowe conditions relating flows/reactions/oscillations.All phenomena considered are treated in accordance with a principle of power transfer optimization (Odum & Pinkerton, 1955). Parametric excitation involves three-body interaction, with one system as energy donor, the pump, another as energy receiving, the idler, and a third as mediator of this energy flow, the signal. A conservation law is mandatory for flows/reactions/oscillations, ωi so that ωpump= ωidler±ωsignal. The macroscopic structure, which sets up the conditions for this law to be in operation, may be of diverse kinds, e.g. membrane-bounded compartments, macromolecules capable of multiple conformations and bound cations, etc. All are non-linear. 相似文献
17.
This paper is concerned with Koopman's (1981) discussion of using the ICDR as a measure of deviation from an additive model of no interaction. This measure has been shown to be zero or slightly negative when the assumptions of no interaction hold in the sufficient-component discrete-cause model. The discussion centers around a theoretical structure of sufficient causes for juvenile-onset diabetes where there is a component cause common to all sufficient causes and two binary factors or risks X and Y are measured (X: Coxsackie B4 infection; Y: HLA4). In this paper, we have extended Koopman's discussion to the case where three or more binary factors X, Y, Z,… are measured. We have considered interaction between factors in every subset and have proved that the ICDR is again either zero or negative when the assumptions of no interaction hold in the sufficient-component cause model. It is supposed that these factors in conjunction will inevitably result in beta-cell destruction together with a set of immunologic conditions that permit dissemination of the enterovirus infection and permit an autoimmune response. 相似文献
18.
The effect of metal ions on human activated Factor X (Factor Xa) hydrolysis of the chromogenic substrate benzoyl-Ile-Glu-Gly-Arg-p-nitroanilide (S2222) was studied utilizing initial rate enzyme kinetics. The divalent metal ions Ca2+, Mn2+, and Mg2+ enhanced Factor Xa amidolytic activity with Km values of 30 μm, 20 μm, and 1.4 mm, respectively. Na+ activation of Factor Xa amidolytic activity was also found. The Km for Na+ activation was 0.31 m. Both the divalent metal ions and Na+ increased the affinity of Factor Xa for S2222 and had no effect on the maximal velocity of the reaction. Other monovalent cations were unable to activate Factor Xa. However, K+ was a competitive inhibitor of the Na+ activation (Ki = 0.14 m). Lanthanide ions inhibited Factor Xa amidolytic activity. Gd3+ inhibition of Factor Xa hydrolysis of S2222 was noncompetitive and had a Ki of 3 μm. The lanthanide ion inhibition could not be reversed by Ca2+ even when Ca2+ was present in a 1000-fold excess over its Km indicating nonidentity of the Factor Xa lanthanide and Ca2+ binding sites. It is concluded that the Factor Xa Ca2+ binding sites have characteristics different from those previously described for the Factor X molecule and that Mg2+, Na+, and K+ may be physiological regulators of Factor Xa activity. 相似文献
19.
20.
Two new Coecobrya species, which were newly collected in 2014, are described from China. Coecobrya
sanmingensis
sp. n. from southeast China (Fujian) is the fourth 1+1 eyed species in the genus; it can be distinguished from other three species by the ciliate chaetae X and X2-4 on the ventral side of head, the abundant chaetae on the trochanteral organ, a large outer tooth on the unguiculus, the absence of smooth manubrial chaetae, and the dorsal chaetotaxy. Coecobrya
qinae
sp. n. from southwest China (Yunnan) is characterized by paddle-like S-chaetae of Ant. III organ, ciliate chaetae X, X2 and X4 posterior to labium, medial macrochaetae on the mesothorax, and 5+5 central and 2+2 lateral macrochaetae on the fourth abdominal segment. An updated key to the Chinese species of Coecobrya is given. 相似文献