Theoretical considerations about carbon isotope distribution in glucose of C3 plants

2004 ◽  
Vol 31 (9) ◽  
pp. 857 ◽  
Author(s):  
Guillaume Tcherkez ◽  
Graham Farquhar ◽  
Franz Badeck ◽  
Jaleh Ghashghaie
Keyword(s):  
Starch Synthesis ◽  
Calvin Cycle ◽  
Mathematical Expression ◽  
C3 Plants ◽  
Fructose 1,6 Bisphosphate ◽  
Theoretical Considerations ◽  
Best Fit ◽  
Photorespiration Rate ◽  
Modelling Approach

The origin of the non-statistical intramolecular distribution of 13C in glucose of C3 plants is examined, including the role of the aldolisation of triose phosphates as proposed by Gleixner and Schmidt (1997). A modelling approach is taken in order to investigate the relationships between the intramolecular distribution of 13C in hexoses and the reactions of primary carbon metabolism. The model takes into account C–C bond-breaking reactions of the Calvin cycle and leads to a mathematical expression for the isotope ratios in hexoses in the steady state. In order to best fit the experimentally-observed intramolecular distribution, the values given by the model indicate that (i), the transketolase reaction fractionates against 13C by 4–7‰ and (ii), depending on the photorespiration rate used for estimations, the aldolase reaction discriminates in favour of 13C by 6‰ during fructose-1,6-bisphosphate production; an isotope discrimination by 2‰ against 13C is obtained when the photorespiration rate is high. Additionally, the estimated fractionations are sensitive to the flux of starch synthesis. Fructose produced from starch breakdown is suggested to be isotopically heavier than sucrose produced in the light, and so the balance between these two sources affects the average intramolecular distribution of glucose derived from stored carbohydrates. The model is also used to estimate photorespiratory and day respiratory fractionations that appear to both depend only weakly on the rate of ribulose-1,5-bisphosphate oxygenation.

Modelling sarcoplasmic reticulum calcium ATPase and its regulation in cardiac myocytes

2009 ◽  
Vol 367 (1896) ◽  
pp. 2181-2202 ◽  
Author(s):  
Jussi T. Koivumäki ◽  
Jouni Takalo ◽  
Topi Korhonen ◽  
Pasi Tavi ◽  
Matti Weckström
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Large Scale ◽  
Cardiac Myocyte ◽  
Model Complexity ◽  
Transport Mechanisms ◽  
Physiological Properties ◽  
Theoretical Considerations ◽  
Sarcoplasmic Reticulum Calcium ◽  
Modelling Approach

When developing large-scale mathematical models of physiology, some reduction in complexity is necessarily required to maintain computational efficiency. A prime example of such an intricate cell is the cardiac myocyte. For the predictive power of the cardiomyocyte models, it is vital to accurately describe the calcium transport mechanisms, since they essentially link the electrical activation to contractility. The removal of calcium from the cytoplasm takes place mainly by the Na + /Ca 2+ exchanger, and the sarcoplasmic reticulum Ca 2+ ATPase (SERCA). In the present study, we review the properties of SERCA, its frequency-dependent and β -adrenergic regulation, and the approaches of mathematical modelling that have been used to investigate its function. Furthermore, we present novel theoretical considerations that might prove useful for the elucidation of the role of SERCA in cardiac function, achieving a reduction in model complexity, but at the same time retaining the central aspects of its function. Our results indicate that to faithfully predict the physiological properties of SERCA, we should take into account the calcium-buffering effect and reversible function of the pump. This ‘uncomplicated’ modelling approach could be useful to other similar transport mechanisms as well.

scholarly journals Phosphofructokinase from bumblebee flight muscle. Molecular and catalytic properties and role of the enzyme in regulation of the fructose 6-phosphate/fructose 1,6-bisphosphate cycle.

1988 ◽  
Vol 263 (33) ◽  
pp. 17527-17533
Author(s):  
A Leite ◽  
J A Neto ◽  
J F Leyton ◽  
O Crivellaro ◽  
H A el-Dorry
Keyword(s):  
Flight Muscle ◽  
Catalytic Properties ◽  
Fructose 1,6 Bisphosphate

scholarly journals The modelling approach determines the carbon footprint of biofuels: the role of LCA in informing decision makers in government and industry

2021 ◽  
pp. 100027
Author(s):  
Miguel Brandão ◽  
Elias Azzi ◽  
Renan.M.L. Novaes ◽  
Annette Cowie
Keyword(s):  
Carbon Footprint ◽  
Decision Makers ◽  
Modelling Approach

scholarly journals Size-mediated, density-dependent cannibalism in the signal crayfish Pacifastacus leniusculus (Dana, 1852) (Decapoda, Astacidea), an invasive crayfish in Britain

Crustaceana ◽  
2017 ◽  
Vol 90 (4) ◽  
pp. 417-435 ◽  
Author(s):  
R. J. Houghton ◽  
C. Wood ◽  
X. Lambin
Keyword(s):  
Relative Size ◽  
Pacifastacus Leniusculus ◽  
Gut Contents ◽  
Size Distributions ◽  
Signal Crayfish ◽  
Density Dependent ◽  
Invasive Crayfish ◽  
The Relationship ◽  
Best Fit

The role of cannibalism in crayfish populations is not well understood, despite being a potentially key density-dependent process underpinning population dynamics. We studied the incidence of cannibalism in an introduced signal crayfish Pacifastacus leniusculus population in a Scottish lowland river in September 2014. Animals were sampled using six different sampling techniques simultaneously, revealing variable densities and size distributions across the site. Cannibalism prevalence was estimated by analysing the gut contents of crayfish >20 mm CL for the presence of crayfish fragments, which was found to be 20% of dissected individuals. When seeking evidence of relationships between the sizes of cannibals and ‘prey’, the density of conspecifics <56% the size of a dissected individual yielded the best fit. The relationship between cannibalism probability and crayfish size and density was equally well described by three different metrics of crayfish density. Cannibalism increased with crayfish size and density but did not vary according to sex. These results suggest that large P. leniusculus frequently cannibalize smaller (prey) conspecifics, and that the probability of cannibalism is dependent upon the relative size of cannibal-to-prey and the density of the smaller crayfish. We suggest that removing large individuals, as targeted by many traditional removal techniques, may lead to reduced cannibalism and therefore a compensatory increase in juvenile survival.

The Role of Empathy in Counseling: Theoretical Considerations

1987 ◽  
pp. 1-20 ◽  
Author(s):  
Gerald A. Gladstein
Keyword(s):  
Theoretical Considerations

scholarly journals Functional cross-talk between allosteric effects of activating and inhibiting ligands underlies PKM2 regulation

2018 ◽  
Author(s):  
Jamie A. Macpherson ◽  
Alina Theisen ◽  
Laura Masino ◽  
Louise Fets ◽  
Paul C. Driscoll ◽  
...  
Keyword(s):  
Enzymatic Activity ◽  
High Activity ◽  
Pyruvate Kinase ◽  
Cross Talk ◽  
Glycolytic Enzyme ◽  
Computational Framework ◽  
Allosteric Inhibitor ◽  
Fructose 1,6 Bisphosphate ◽  
Low Activity

ABSTRACTAllosteric regulation is central to the role of the glycolytic enzyme pyruvate kinase M2 (PKM2) in cellular metabolism. Multiple activating and inhibitory allosteric ligands regulate PKM2 activity by controlling the equilibrium between high activity tetramers and low activity dimers and monomers. However, it remains elusive how allosteric inputs upon simultaneous binding of different ligands are integrated to regulate PKM2 activity. Here, we show that, in the presence of the allosteric inhibitor L-phenylalanine (Phe), the activator fructose 1,6-bisphosphate (FBP) can induce PKM2 tetramerisation, but fails to maximally increase enzymatic activity. Guided by a new computational framework we developed to identify residues that mediate FBP-induced allostery, we generated two PKM2 mutants, A327S and C358A, in which activation by FBP remains intact but cannot be attenuated by Phe. Our findings demonstrate a role for residues involved in FBP-induced allostery in enabling the integration of allosteric input from Phe and reveal a mechanism that underlies the co-ordinate regulation of PKM2 activity by multiple allosteric ligands.

Abstract 20: Resident Cardiac Stem Cell Growth Determines the Number of Ventricular Cardiomyocytes in the Mouse Heart

2012 ◽  
Vol 111 (suppl_1) ◽  
Author(s):  
Barbara Ogórek ◽  
João Ferreira-Martins ◽  
Donato Cappetta ◽  
Alex Matsuda ◽  
Sergio Signore ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Late Gestation ◽  
Primary Data ◽  
Mouse Heart ◽  
Lineage Specification ◽  
Exponential Equation ◽  
Cell Organization ◽  
Parenchymal Cells ◽  
Best Fit

The objective of this study was to determine the role of c-kit-positive cardiac stem cells (CSCs) in the formation of the heart during prenatal life, and immediately after birth. Mice in which EGFP is under the control of the c-kit-promoter were employed to measure the number of CSCs (Ns), the fraction of cycling MCM5-positive CSCs (f) and the length of the cell cycle (Ts) in CSCs. The number of CSCs committed to the myocyte lineage (LCC: lineage committed cells) included myocyte progenitors (c-kit-positive, Nkx2.5-positive cells), myocyte precursors (c-kit-positive, Nkx2.5-positive, and α-sarcomeric actin-positive cells) and replicating amplifying myocytes (c-kit-negative, Nkx2.5-positive, α-sarcomeric actin-positive, and MCM5-positive cells). These variables derived from CSC growth and lineage specification were evaluated to define the rate of formation of terminally differentiated myocytes (r). Based on a hierarchically structured cell organization, the rate of entry (Rs) of CSCs into the cell cycle was computed from Rs = f x (Ns/Ts), and the rate of generation of mature myocytes, r, was obtained from r = Rs x 2 Gt = ((f x Ns)/Ts) x 2 Gt . The exponent Gt defines the number of transit generations, i.e., the number of divisions that one CSC has to go through before it acquires the terminally differentiated myocyte phenotype. To validate this scenario and establish the number of post-mitotic myocytes formed, the primary data listed above were collected at E9, E14, E19 and P1. The number of mature cardiomyocytes generated by 1 CSC in 1 day was 1.1 x 10 3 , 20 x 10 3 , 501 x 10 3 , and 440 x 10 3 at E9, E14, E19 and P1, respectively. The total number of myocytes (Nm) formed from E9 to E14, E19 and P1 was derived from an exponential equation with the best fit to the experimental data: Nm = exp (0.69 x t) where Nm is the number of myocytes and t is time in days. Accordingly, CSCs generated 1 x 10 5 , 1 x 10 6 and 1.8 x 10 6 myocytes at from E9 to E14, E19 and P1, respectively. These values accounted for all parenchymal cells present at mid and late gestation and in the neonatal heart measured morphometrically. Thus, the expansion of the myocyte mass during embryonic, fetal and immediate postnatal development is controlled by activation, growth and differentiation of resident c-kit-positive CSCs.

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