A Comparison of Bimolecular Reaction Models for Stochastic Reaction–Diffusion Systems

Stochastic reaction–diffusion models have become an important tool in studying how both noise in the chemical reaction process and the spatial movement of molecules influences the behavior of biological systems. There are two primary spatially-continuous models that have been used in recent studies: the diffusion limited reaction model of Smoluchowski, and a second approach popularized by Doi. Both models treat molecules as points undergoing Brownian motion. The former represents chemical reactions between two reactants through the use of reactive boundary conditions, with two molecules reacting instantly upon reaching a fixed separation (called the reaction-radius). The Doi model uses reaction potentials, whereby two molecules react with a fixed probability per unit time, λ, when separated by less than the reaction radius. In this work, we study the rigorous relationship between the two models. For the special case of a protein diffusing to a fixed DNA binding site, we prove that the solution to the Doi model converges to the solution of the Smoluchowski model as λ→∞, with a rigorous $O(\lambda^{-\frac{1}{2} + \epsilon})$ error bound (for any fixed ?>0). We investigate by numerical simulation, for biologically relevant parameter values, the difference between the solutions and associated reaction time statistics of the two models. As the reaction-radius is decreased, for sufficiently large but fixed values of λ, these differences are found to increase like the inverse of the binding radius.     

Reaction–diffusion model of atherosclerosis development

Atherosclerosis begins as an inflammation in blood vessel walls (intima). The inflammatory response of the organism leads to the recruitment of monocytes. Trapped in the intima, they differentiate into macrophages and foam cells leading to the production of inflammatory cytokines and further recruitment of white blood cells. This self-accelerating process, strongly influenced by low-density lipoproteins (cholesterol), results in a dramatic increase of the width of blood vessel walls, formation of an atherosclerotic plaque and, possibly, of its rupture. We suggest a 2D mathematical model of the initiation and development of atherosclerosis which takes into account the concentration of blood cells inside the intima and of pro- and anti-inflammatory cytokines. The model represents a reaction-diffusion system in a strip with nonlinear boundary conditions which describe the recruitment of monocytes as a function of the concentration of inflammatory cytokines. We prove the existence of travelling waves described by this system and confirm our previous results which suggest that atherosclerosis develops as a reaction-diffusion wave. The theoretical results are confirmed by the results of numerical simulations.     

Chemical Studies on Amino––Carbonyl Reaction

The 3-deoxy-n-pentosone (I) was isolated from the browning degradation mixture of N-n-xy1osy1-n-butylamine by the action of acetic acid at 55°C. The 3-deoxy-d-erythrohexosone (IIa) and the 3-deoxy-n-threohexosone (IIb) were also prepared by degradation of the corresponding N-glycosyl-n-butylamine. The 3-deoxy-d-pentosone was characterized as the 2,4-dinitrophenylosazone and its diacetate, and the p-nitrophenylosazone. The two 3-deoxy-d-hexosones were also characterized as the analogous derivatives. The three 3-deoxyosones gave positive color reactions with 2-thiobarbituric acid.

As one of the intermediates in 3-deoxyosone formation from N-glycoside, 1,2-eno1 form of 1-deoxy-1-n-butylamino-2-ketose (IV) was proposed.     

Chemical Studies on Amino—Carbonyl Reaction

When N-n-butyl-D-xylosylamine was heated with acetic acid in methanol at 55~70°G, it decomposed to N-n-butyIpyrrole-2-aldehyde,** through 3-deoxy-d-pentosulose as an intermediate. d-Xylose and methylamine in neutralized aqueous solution at 65~100°C also formed N-methylpyrrole-2-aldehyde. N-n-Butyl-l-rhamnosylamine, in a mixture of methanol and acetic acid, formed the corresponding pyrrolealdehyde, l-n-butyl-5-methylpyrrole-2- aldehyde, at the almost same rate as did N-xyloside. On the contrary, N-n-butyl-d-glucosylamine, under the same condition, did not form any detectable amount of the corresponding pyrrolealdehyde, but formed complicated products. A formation mechanism of the pyrrolealdehydes from 3-deoxyosulose and amine was proposed.     

Mutagen Formation in the Nitrite—Piperic Acid Reaction

A morphological mutant of Neurospora crassa, which showed great changes in cell wall β-glucan structures, was obtained. The mutant lacked spore-forming ability. Chemical analysis indicated that the mutant cell walls had more carbohydrates and less proteins than the wild type. In the structural polymers of cell walls, heteroglycan and chitin were not apparently changed in their sugar composition and structures. On the other hand, the alkali-soluble β-glucan of this mutant showed significant changes in the chemical structure, particularly, the number and length of branches. The mutant glucan had about 2.5 times as many branches as that from wild type and the number of 1,3-linked glucose residues was greatly reduced.     

聚合酶链反应（Polymerase Chain Reaction，PCR）

PCR是80年代中期发展起来的体外核酸扩增技术。它具有特异、敏感、产率高、快速、简便、重复性好、易自动化等突出的优点;能在一个试管内将所要研究的目的基因或某一DNA片段于数小时内扩增至十万乃至百万倍,使肉眼能直接观察和判断;可从一根毛发、一滴血、甚至一个细胞中扩增出足量的DNA供分析研究和检测鉴定。过去几天几星期才能做到的事情,用PCR几小时便可完成。PCR技术是生物医学领域中的一项革命性创举和里程碑。     

Condensation Reaction Occurring during Plastein Formation by α-Chymotrypsin

An investigation was conducted on myosin and actin-activated heavy meromyosin (HMM) ATPase activities in normal porcine muscle stored for varying periods of time after death. Studies were also made on temperature dependent myosin ATPase, initial burst of ATPase and actin-activated HMM ATPase in normal and in pale, soft and exudative (PSE) porcine muscle. The maximum velocity of acto-HMM ATPase of normal muscle decreased considerably with postmortem time, while the apparent dissociation constant decreased slightly. The maximum velocity of acto-HMM ATPase of postmortem normal muscle was approximately two-times larger than that of the corresponding PSE muscle. However, almost no difference was found in the apparent dissociation constant. The size of the initial burst of phosphate-liberation of myosin prepared from normal muscle was approximately 1.2 mol/mol of myosin and from PSE muscle 0. It is assumed that the lack of contractility of PSE muscle was brought about by two basic myosin malfunctions: one, the irreversible binding of myosin to actin filament and the other, the functional damage of myosin ATPase, responsible for the formation of phosphorylated complex, even when dissociable.     

Does Observation of Postural Imbalance Induce a Postural Reaction?

Background

Several studies bring evidence that action observation elicits contagious responses during social interactions. However automatic imitative tendencies are generally inhibited and it remains unclear in which conditions mere action observation triggers motor behaviours. In this study, we addressed the question of contagious postural responses when observing human imbalance.

Methodology/Principal Findings

We recorded participants'' body sway while they observed a fixation cross (control condition), an upright point-light display of a gymnast balancing on a rope, and the same point-light display presented upside down. Our results showed that, when the upright stimulus was displayed prior to the inverted one, centre of pressure area and antero-posterior path length were significantly greater in the upright condition compared to the control and upside down conditions.

Conclusions/Significance

These results demonstrate a contagious postural reaction suggesting a partial inefficiency of inhibitory processes. Further, kinematic information was sufficient to trigger this reaction. The difference recorded between the upright and upside down conditions indicates that the contagion effect was dependent on the integration of gravity constraints by body kinematics. Interestingly, the postural response was sensitive to habituation, and seemed to disappear when the observer was previously shown an inverted display. The motor contagion recorded here is consistent with previous work showing vegetative output during observation of an effortful movement and could indicate that lower level control facilitates contagion effects.     

Reconstitution of Photosystem Ⅱ Reaction Center with Cu-ChlorophyⅡ a

An Isolated photosystem （PS） II reaction center （RC） with altered pigment content was obtained by chemical exchange of native chlorophyll a （Chl） with externally added Cu-Chl a （Cu-Chl）. Pigment composition and spectroscopic properties of the RC exchanged with Cu-Chl were compared with native RC and RC treated with Chl In the same way. High-performance liquid chromatography analysis showed approximately 0.5 Cu-Chl per two pheophytln in the Cu-Chl-reconstltuted RC preparation. Insertion of Cu-Chl resulted in a decrease In absorption at 670 nm and an Increase at 660 nm, suggesting that the peripheral Chl may have been displaced. Fluorescence emission spectra of the Cu-Chl-reconstituted RC displayed a marked decrease In fluorescence yield and a blue shift of the band maximum, accompanied by the appearance of a broad peak at a shorter wavelength, Indicating that energy transfer In the modified RC was disturbed by Cu-Chl, a quencher of the excited state. However, there were few differences in the circular dichrolsm （CD） spectra, suggesting that the arrangement of pigments and proteins responsible for the CD signal was not significantly affected. In addition, no obvious change In peptlde components was found after the exchange procedure.     

Bidirectional Electron Transfer in the Reaction Centre of Photosystem Ⅰ

In the past decade light-induced electron transfer reactions in photosystem Ⅰ have been the subject of intensive investigations that have led to the elucidation of some unique characteristics,the most striking of which is the existence of two parallel,functional,redox active cofactors chains.This process is generally referred to as bidirectional electron transfer.Here we present a review of the principal evidences that have led to the uncovering of bidirectionality in the reaction centre of photosystem Ⅰ.A special focus is dedicated to the results obtained combining time-resolved spectroscopic techniques,either difference absorption or electron paramagnetic resonance,with molecular genetics,which allows,through modification of the binding of redox active cofactors with the reaction centre subunits,an effect on their physical-chemical properties.