Hyperchirality: a mathematically convenient and biochemically possible model for the kinetics of morphogenesis

Two general problems in morphogenesis are discussed: (a) scaling of the repeating unit of a pattern to the overall size of the organism; (b) biochemically realistic mechanisms for highly localized autocatalysis to produce pattern on a wall or membrane of a single cell. These problems are approached by comparing the Mills (1932) model for spontaneous resolution by bimolecular autocatalysis in formation of a pair of enantiomers (D and L) with the Turing (1952) model for morphogenesis by catalytic and inhibitory interactions of two morphogens (X and Y) very unsymmetrically matched in kinetic properties. A model for a morphogen M is proposed in the form of a pair of enantiomers M D and M L , with the out-of-equilibrium morphogen concentration variable in the Turing equations being the optical asymmetry M = M D — M L . Formation of M out of a precursor (pro-morphogen A), with two reactions A → M D and A → M L to control the single variable M , allows the Turing theory to encompass a variety of ways in which pattern unit scales with overall size. To this end, formation of morphogens by parallel reactions exceeding in number the morphogen concentration variables is a general principle independent of the reality of this specific model. More tentatively, the model is put forward as a possible real structure for morphogens on a cell wall or membrane. Both M D and M L must be present. It is suggested that the lowest level of organization at which structures of two chiralities might be found, when their molecules are of one chirality only, is the attachment of an enzyme polymer, with definite quaternary structure, to the cell surface. The enantiomers may then be the same polymeric assembly facing inwards or outwards. The word hyperchirality is suggested for this kind of asymmetry. Some morphogenetic features of the single-celled desmid alga Micrasterias are discussed, to illustrate the geometrical problems of translating morphogen kinetics into development of shape, and to show that the number of active morphogens and the dimensionality of the space in which they act may decrease during development.

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Thermal Decomposition Kinetics of Torrefied Oil Palm Empty Fruit Bunch Briquettes

Chemistry & Chemical Technology ◽

10.23939/chcht10.03.325 ◽

2016 ◽

Vol 10 (3) ◽

pp. 325-328 ◽

Cited By ~ 1

Author(s):

Bemgba Nyakuma ◽

◽

Arshad Ahmad ◽

Anwar Johari ◽

Tuan Abdullah ◽

...

Keyword(s):

Thermal Decomposition ◽

Oil Palm ◽

Decomposition Kinetics ◽

Thermal Decomposition Kinetics ◽

Kinetic Properties ◽

Tg Analysis ◽

Empty Fruit Bunches ◽

Thermal Lag ◽

Profile Characteristics ◽

Kinetics Of

The study is aimed at investigating the thermal behavior and decomposition kinetics of torrefied oil palm empty fruit bunches (OPEFB) briquettes using a thermogravimetric (TG) analysis and the Coats-Redfern model. The results revealed that thermal decomposition kinetics of OPEFB and torrefied OPEFB briquettes is significantly influenced by the severity of torrefaction temperature. Furthermore, the temperature profile characteristics; Tonset, Tpeak, and Tend increased consistently due to the thermal lag observed during TG analysis. In addition, the torrefied OPEFB briquettes were observed to possess superior thermal and kinetic properties over the untorrefied OPEFB briquettes. It can be inferred that torrefaction improves the fuel properties of pelletized OPEFB for potential utilization in bioenergy conversion systems.

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Kinetics of Na+/H+ exchange in vascular smooth muscle cells from WKY and SHR: effects of phorbol ester

AJP Cell Physiology ◽

10.1152/ajpcell.1995.268.1.c14 ◽

1995 ◽

Vol 268 (1) ◽

pp. C14-C20 ◽

Cited By ~ 19

Author(s):

G. Hoffmann ◽

Y. Ko ◽

A. Sachinidis ◽

B. O. Gobel ◽

H. Vetter ◽

...

Keyword(s):

Smooth Muscle ◽

Vascular Smooth Muscle ◽

Smooth Muscle Cells ◽

Vascular Smooth Muscle Cells ◽

Muscle Cells ◽

Maximal Activity ◽

Hill Coefficient ◽

Kinetic Properties ◽

Wistar Kyoto ◽

Kinetics Of

The kinetic properties of Na+/H+ exchange were investigated in vascular smooth muscle cells (VSMC) in culture from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Antiport activity was measured in 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein-loaded cells after nigericin-induced cytosolic acidification. Studies were performed without (control) and with pretreatment of the cells with phorbol 12-myristate 13-acetate (PMA; 200 nM). Na+/H+ exchange markedly differed between the two strains with lower Hill coefficients [1.56 +/- 0.17 (SE) vs. 2.62 +/- 0.36] and higher maximal activity (Vmax) values (55.85 +/- 5.24 vs. 31.11 +/- 2.38 mmol H+.l-1.min-1) in SHR compared with WKY cell lines. PMA markedly altered the antiport kinetics in WKY VSMC with a decrease in the Hill coefficient (1.75 +/- 0.14) without affecting Vmax (31.88 +/- 1.55 mmol H+.l-1.min-1). In VSMC from SHR, PMA had no effect on the kinetic variables investigated. Thus two kinetic abnormalities are present with respect to Na+/H+ antiport activity in VSMC from SHR compared with WKY, i.e., increased Vmax and decreased Hill coefficient. The observation that PMA does not affect the kinetics of the Na+/H+ antiport in VSMC from SHR suggests a marked degree of antiporter prestimulation in this animal model of genetic hypertension.

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The kinetics of action of acetylcholine antagonists in smooth muscle

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1966.0045 ◽

1966 ◽

Vol 164 (996) ◽

pp. 488-510 ◽

Cited By ~ 76

Keyword(s):

Smooth Muscle ◽

Binding Capacity ◽

Equilibrium Constants ◽

Dose Effect ◽

Analogue Computer ◽

Kinetic Properties ◽

Receptor Complexes ◽

Rate Limiting Step ◽

Drug Receptor ◽

Kinetics Of

The rate-limiting step in recovery of acetylcholine sensitivity in smooth muscle after exposure to atropine or hyoscine could be the dissociation of drug-receptor complexes (dissociationlim ited model) or diffusion of drug away from the neighbourhood of the receptors (biophase model). These two models differ in the details of the predicted kinetics of development and decline of antagonism. Their theoretical kinetic properties have been worked out mathematically with the aid of an analogue computer, and com pared with experimental measurements made in guinea-pigileum longitudinal muscle preparations. The kinetic properties of antagonists applied singly could be explained either by the dissociation-limited model, or by the biophase model, provided that the size of the biophase bore a certain relation to the binding capacity of the receptors. In studies of the interaction of fastand slow-acting antagonists, it was found that the dissociation-limited model could alone account for the observed effects. It was concluded that the kinetics of action of hyoscine and atropine reflected their rate of reaction with receptors, an d that measurements of antagonist kinetics were a valid guide to drug-receptor rate constants. A consequence of the dissociation-limited model, that persistent antagonists should fail to show the classical parallel shift of log-dose effect curves when tested against agonists of low efficacy, was borne out experimentally, and this effect was used to estimate indirectly the equilibrium constants of alkyltrimethylammonium salts.

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THE TIME OF SYNTHESIS AND THE CONSERVATION OF MITOSIS-RELATED PROTEINS IN CULTURED HUMAN AMNION CELLS

The Journal of Cell Biology ◽

10.1083/jcb.34.1.97 ◽

1967 ◽

Vol 34 (1) ◽

pp. 97-110 ◽

Cited By ~ 43

Author(s):

Jesse E. Sisken ◽

Elaina Wilkes

Keyword(s):

Time Lapse ◽

Major Effect ◽

Human Amnion ◽

Daughter Cells ◽

Low Concentrations ◽

Associated Proteins ◽

A Cell ◽

Quantitative Analyses ◽

Related Proteins ◽

Kinetics Of

p-Fluorophenylalanine (PFPA), an analogue of phenylalanine which may be incorporated into proteins, increases the duration of mitosis. In the present experiments, based upon quantitative analyses of time-lapse cinemicrographic films, brief treatments of cells with PFPA are shown to affect the duration of metaphase in only those cells which enter division during or shortly after treatment. The offspring of cells with prolonged metaphases also tend to have prolonged metaphases. Analyses of the kinetics of the appearance of prolonged metaphases indicate that some protein specifically associated with mitosis is synthesized primarily during a period which corresponds closely to G2. The manner in which the defect is passed on to daughter cells indicates that the protein involved is conserved and reutilized by daughter cells for their subsequent divisions. Comparable experiments performed with low concentrations of puromycin indicate that the major effect of PFPA is due to its incorporation into protein rather than its ability to inhibit protein synthesis. The fact that puromycin-induced effects can also be passed on to daughter cells is interpreted to mean that cells make only specific amounts of some mitosis-associated proteins and that if a cell "inherits" a deficiency in such protein it is not able to compensate for the deficiency.

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Kinetics of homogeneous chemical reactions

Thermodynamics and Kinetics in Materials Science ◽

10.1093/oso/9780198528036.003.0010 ◽

2005 ◽

Author(s):

Boris S. Bokstein ◽

Mikhail I. Mendelev ◽

David J. Srolovitz

Keyword(s):

Chemical Reactions ◽

Irreversible Thermodynamics ◽

Kinetic Process ◽

Chemical Reaction Kinetics ◽

Long Time ◽

Homogeneous Chemical ◽

Parallel Reactions ◽

Diffusive Processes ◽

Kinetics Of

Kinetics considers the rates of different processes. Chemical kinetics refers to the rates and mechanisms of chemical reactions and mass transfer (diffusion). Recall that since thermodynamic equilibrium implies that the rates of all processes are zero, time is not a thermodynamic variable. Rather, time is the new parameter introduced by the consideration of kinetic processes. The rate of a kinetic process and how it depends on time is determined, in part, by the degree of the deviation from equilibrium. If the deviation from equilibrium is small, the rate decreases (without changing sign) as the system approaches equilibrium. If the deviation from equilibrium is large, the situation is more complicated. For example, non-monotonic (including oscillatory) processes are possible. The sign of the rate can change during such processes; that is, the reaction can proceed in one direction and then the other. Additionally, if the deviation from equilibrium is large, small changes to the system can produce very large changes in the rate of the kinetic process (i.e. chaos). Non-equilibrium, yet nearly stationary states of the system can arise (i.e. states that exist for a very long time). Finally, if the deviation from equilibrium is very large, the system can explode (i.e. the process continues to accelerate with time). In this chapter, we develop a formal description of the kinetics of rather simple chemical reactions. Consecutive and parallel reactions will also be considered here. A more general approach (irreversible thermodynamics) will be considered in Chapter 9. In Chapter 10, we examine diffusive processes. Then, in Chapter 11, we consider the kinetics of heterogeneous processes. In order to start the study of chemical reaction kinetics, we must first define what we mean by the rate of reaction. Consider the following homogeneous reaction: . . . Cl2 + 2NO → 2NOCl. (8.1) . . .

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In Vivo and in Vitro Proliferation Kinetics of Sarcoma 180 in Solid Form

Tumori Journal ◽

10.1177/030089167205800504 ◽

1972 ◽

Vol 58 (5) ◽

pp. 335-339 ◽

Cited By ~ 3

Author(s):

Rosella Silvestrini ◽

Ornella Sanfilippo ◽

Luigi Lenaz

Keyword(s):

Double Labelling ◽

Pulse Labelling ◽

Sarcoma 180 ◽

In Vitro Proliferation ◽

Proliferation Kinetics ◽

Human Solid Tumors ◽

A Cell ◽

Kinetics Of

In order to obtain data for setting up a rapid and relatively inexpensive method for studying the proliferation kinetics of human solid tumors, we have determined the kinetic parameters of an experimental solid tumor (Sarcoma 180). The curve of labelled mitosis after pulse labelling with 3H thymidine and the 3H and 14C thymidine double labelling technic on tumor samples incubated in vitro with the labelled precursors were used. A method of digestion of the tissue with hyaluronidase to obtain a cell suspension is described. This method allows easy identification of cells labelled with 3H or 14C thymidine. The two methods yielded reproducible results, the labelling index being 45%, and the duration of S phase 9.9 hours. The in vitro double labelling method with subsequent hyaluronidase digestion is proposed for studying the proliferation kinetics of solid malignancies.

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Thermodynamics and Kinetics of Bulk Metallic Glass

MRS Bulletin ◽

10.1557/mrs2007.122 ◽

2007 ◽

Vol 32 (8) ◽

pp. 620-623 ◽

Cited By ~ 161

Author(s):

R. Busch ◽

J. Schroers ◽

W. H. Wang

Keyword(s):

Metallic Glasses ◽

Pure Metal ◽

Glass Forming Ability ◽

Kinetic Properties ◽

Size Mismatch ◽

Atomic Size ◽

Glass Forming ◽

Thermodynamics And Kinetics ◽

Metal Melts ◽

Kinetics Of

AbstractBulk metallic glasses (BMGs) are multicomponent alloys with typically three to five components with large atomic size mismatch and a composition close to a deep eutectic. Packing in BMG liquids is very dense, with a low content of free volume resulting in viscosities that are several orders of magnitude higher than in pure metal melts. The dense packing accomplished by structural and chemical atomic ordering also brings the BMG-forming liquid energetically and entropically closer to its corresponding crystalline state. These factors lead to slow crystallization kinetics and consequentially to high glass-forming ability. This article highlights the thermodynamic and kinetic properties of BMGs and their contributions to extraordinarily high glass-forming ability. Some possible links with mechanical properties are also suggested.

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The effects of 5α-dihydrotestosterone on the kinetics of cell proliferation in rat prostate

Biochemical Journal ◽

10.1042/bj1420483 ◽

1974 ◽

Vol 142 (3) ◽

pp. 483-489 ◽

Cited By ~ 9

Author(s):

Barry Lesser ◽

Nicholas Bruchovsky

Keyword(s):

Cell Cycle ◽

Cell Proliferation ◽

Cellular Growth ◽

Velocity Sedimentation ◽

Growth Fraction ◽

Subcutaneous Injections ◽

Daughter Cells ◽

A Cell ◽

Rat Prostate ◽

Kinetics Of

The regenerating rat prostate was used as an experimental model to determine the effects of 5α-dihydrotestosterone on certain parameters of cell proliferation, including the duration of the phases of the cell cycle and the size of the cellular growth fraction. Rats castrated 7 days previously were treated with daily subcutaneous injections of 5α-dihydrotestosterone for 14 days; 48h after the beginning of therapy, cells in the process of DNA synthesis were labelled with a single injection of radioactive thymidine and the progress of these cells through the division cycle was observed. Cell-cycle analysis was performed by fractionating prostatic nuclei according to their position in the cell cycle by using the technique of velocity sedimentation under unit gravity. The results indicate that during regeneration the cell population undergoes 1.8 doublings with a doubling time of 40h, and that the process involves almost four rounds of cell division with a cell-generation time of 20h. The growth fraction at any time is about 0.5, and about half the daughter cells produced do not re-enter the proliferative cycle. All cells present at the start of regeneration eventually undergo at least one division during the course of regeneration, although any given cell can divide from one to four times.

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The mechanochemistry of the kinesin-2 KIF3AC heterodimer is related to strain-dependent kinetic properties of KIF3A and KIF3C

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1916343117 ◽

2020 ◽

Vol 117 (27) ◽

pp. 15632-15641

Author(s):

Brandon M. Bensel ◽

Michael S. Woody ◽

Serapion Pyrpassopoulos ◽

Yale E. Goldman ◽

Susan P. Gilbert ◽

...

Keyword(s):

Single Molecule ◽

Mechanical Load ◽

Optical Trap ◽

Kinetic Properties ◽

Dependent Manner ◽

Force Sensitivity ◽

Mammalian Neuron ◽

Kinetics Of ◽

Strain Dependent ◽

Transport Potential

KIF3AC is a mammalian neuron-specific kinesin-2 implicated in intracellular cargo transport. It is a heterodimer of KIF3A and KIF3C motor polypeptides which have distinct biochemical and motile properties as engineered homodimers. Single-molecule motility assays show that KIF3AC moves processively along microtubules at a rate faster than expected given the motility rates of the KIF3AA and much slower KIF3CC homodimers. To resolve the stepping kinetics of KIF3A and KIF3C motors in homo- and heterodimeric constructs and determine their transport potential under load, we assayed motor activity using interferometric scattering microscopy and optical trapping. The distribution of stepping durations of KIF3AC molecules is described by a rate (k1= 11 s−1) without apparent kinetic asymmetry. Asymmetry was also not apparent under hindering or assisting mechanical loads in the optical trap. KIF3AC shows increased force sensitivity relative to KIF3AA yet is more capable of stepping against mechanical load than KIF3CC. Interestingly, the behavior of KIF3C mirrors prior studies of kinesins with increased interhead compliance. Microtubule gliding assays containing 1:1 mixtures of KIF3AA and KIF3CC result in speeds similar to KIF3AC, suggesting the homodimers mechanically impact each other’s motility to reproduce the behavior of the heterodimer. Our observations are consistent with a mechanism in which the stepping of KIF3C can be activated by KIF3A in a strain-dependent manner, similar to application of an assisting load. These results suggest that the mechanochemical properties of KIF3AC can be explained by the strain-dependent kinetics of KIF3A and KIF3C.

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