Ping-pong Research Articles

A biophysically based mathematical model for the catalytic mechanism of glutathione reductase

Glutathione reductase (GR) catalyzes the reduction of oxidized glutathione (GSSG) to reduced glutathione (GSH) using NADPH as the reducing cofactor, and thereby maintains a constant GSH level in the system. GSH scavenges superoxide (O2−) and hydroxyl radicals (OH) nonenzymatically or by serving as an electron donor to several enzymes involved in reactive oxygen species (ROS) detoxification. In either case, GSH oxidizes to GSSG and is subsequently regenerated by the catalytic action of GR. Although the GR kinetic mechanism has been extensively studied under various experimental conditions with variable substrates and products, the catalytic mechanism has not been studied in terms of a mechanistic model that accounts for the effects of the substrates and products on the reaction kinetics. The aim of this study is therefore to develop a comprehensive mathematical model for the catalytic mechanism of GR. We use available experimental data on GR kinetics from various species/sources to develop the mathematical model and estimate the associated model parameters. The model simulations are consistent with the experimental observation that GR operates via both ping–pong and sequential branching mechanisms based on relevant concentrations of its reaction substrate GSSG. Furthermore, we show the observed pH-dependent substrate inhibition of GR activity by GSSG and bimodal behavior of GR activity with pH. The model presents a unique opportunity to understand the effects of products on the kinetics of GR. The model simulations show that under physiological conditions, where both substrates and products are present, the flux distribution depends on the concentrations of both GSSG and NADP+, with ping–pong flux operating at low levels and sequential flux dominating at higher levels. The kinetic model of GR may serve as a key module for the development of integrated models for ROS-scavenging systems to understand protection of cells under normal and oxidative stress conditions.

Kinetic modeling of lipase‐catalyzed esterification reaction between oleic acid and trimethylolpropane: A simplified model for multi‐substrate multi‐product ping–pong mechanisms

Kinetic models are among the tools that can be used for optimization of biocatalytic reactions as well as for facilitating process design and upscaling in order to improve productivity and economy of these processes. Mechanism pathways for multi-substrate multi-product enzyme-catalyzed reactions can become very complex and lead to kinetic models comprising several tens of terms. Hence the models comprise too many parameters, which are in general highly correlated and their estimations are often prone to huge errors. In this study, Novozym(®) 435 catalyzed esterification reaction between oleic acid (OA) and trimethylolpropane (TMP) with continuous removal of side-product (water) was carried out as an example for reactions that follow multi-substrate multi-product ping-pong mechanisms. A kinetic model was developed based on a simplified ping-pong mechanism proposed for the reaction. The model considered both enzymatic and spontaneous reactions involved and also the effect of product removal during the reaction. The kinetic model parameters were estimated using nonlinear curve fitting through unconstrained optimization methodology and the model was verified by using empirical data from different experiments and showed good predictability of the reaction under different conditions. This approach can be applied to similar biocatalytic processes to facilitate their optimization and design.

Enzymatic oxidation of rutin by horseradish peroxidase: Kinetic mechanism and identification of a dimeric product by LC–Orbitrap mass spectrometry

Flavonoid oxidation is important issue in food processing and quality. The kinetic mechanism of enzymatic oxidation of rutin by horseradish peroxidase (HRP) was studied. Rutin oxidation reaction was followed by recording of spectral changes over the time at 360nm. The studied oxidation is mostly enzymatic and less part non-enzymatic. The reaction with HRP has a higher rate compared with the reaction without of HRP, whereby is part of non-enzymatic reaction about 10% of the total reaction. Kinetic parameters were determined from graphics of linear Michaelis–Menten equation, and it was found that investigated reactions of rutin oxidation by HRP take place in a ping–pong kinetic mechanism. High resolution HPLC–MS analysis of the mixture of oxidized products of rutin revealed the presence of rutin dimer. Because of widely distribution of rutin as well as presence of peroxidases and hydrogen peroxide in fresh foods identification of this enzymatic modification product can be beneficial for foods quality and safety.

An evaluation of the outdoor table tennis initiative pilot programme in London: ‘ping pong in the fresh air how does that work?’

This article examines the findings from an evaluation of the English Table Tennis Association outdoor table tennis pilot initiative in London. Ethnographic participant observation fieldwork was conducted, alongside semi-structured interviews with project and local partner staff to explore the impact and effectiveness of the scheme. The project aspiration was to develop a new entry route into the sport of table tennis, using an innovative new format of the game in park facilities. The project challenged established principles of sports development to encourage self-organised participation, raise the profile of the sport and attract new participants to this form of physical activity in a park setting. Results from the pilot programme evaluation illustrated that participants had engaged in multiple forms of self-organised play, usage of the tables were high and that there were minimal barriers to participation. Future challenges include how to link this initiative with wider national governing body sports development plans, harnessing the profile raising potential of the scheme and the development of opportunities and participants that were created through the scheme.

“Verbal Ping Pong” as Culturally Congruent Communication: Maximizing African American Students' Access and Engagement as Socially Just Teaching

African American youth have been disciplined and dismissed from classrooms for engaging in culturally-based communication practices that teachers misinterpret and perceive as disruptive. Teachers have significant power in how they communicate with their students. White teachers should be especially aware of this power because misunderstandings around communication often stem from cultural differences. This study illustrates the promising practice of a white teacher who integrated African American students' culturally-based literacy practice of “verbal ping pong” into English subject matter instruction. Ethnographic methods that foreground the perspectives of student participants illuminated the significance of this highly interactive discourse, while discourse analysis showed how it functioned as culturally congruent communication to promote students' access to classroom discourse and engagement in subject matter learning. By showing how culturally congruent communication can provide equitable access to learning opportunities for all students, this study renders a promising representation of socially just pedagogy.

Substrate Channel Flexibility in Pseudomonas aeruginosa MurB Accommodates Two Distinct Substrates

Biosynthesis of UDP-N-acetylmuramic acid in bacteria is a committed step towards peptidoglycan production. In an NADPH- and FAD-dependent reaction, the UDP-N-acetylglucosamine-enolpyruvate reductase (MurB) reduces UDP-N-acetylglucosamine-enolpyruvate to UDP-N-acetylmuramic acid. We determined the three-dimensional structures of the ternary complex of Pseudomonas aeruginosa MurB with FAD and NADP+ in two crystal forms to resolutions of 2.2 and 2.1 Å, respectively, to investigate the structural basis of the first half-reaction, hydride transfer from NADPH to FAD. The nicotinamide ring of NADP+ stacks against the si face of the isoalloxazine ring of FAD, suggesting an unusual mode of hydride transfer to flavin. Comparison with the structure of the Escherichia coli MurB complex with UDP-N-acetylglucosamine-enolpyruvate shows that both substrates share the binding site located between two lobes of the substrate-binding domain III, consistent with a ping pong mechanism with sequential substrate binding. The nicotinamide and the enolpyruvyl moieties are strikingly well-aligned upon superimposition, both positioned for hydride transfer to and from FAD. However, flexibility of the substrate channel allows the non-reactive parts of the two substrates to bind in different conformations. A potassium ion in the active site may assist in substrate orientation and binding. These structural models should help in structure-aided drug design against MurB, which is essential for cell wall biogenesis and hence bacterial survival.

G03(P) Craniotabes: Time For an Old Physical Sign to Be Put to Use?

AimsCraniotabes describes softness of the infant’s cranial bones, causing a ‘ping pong ball’ effect after minimal pressure is applied. Exact causes of this phenomenon are not clear. This paper aimed...

Dihydrodipicolinate Synthase from E. coli: Characterization of Arginine 138 by Site‐Directed Mutagenesis

Dihydrodipicolinate synthase catalyzes the formation of dihydropicolinate from pyruvate and L‐aspartate‐β‐semialdehyde (ASA). The enzyme catalyzes the first committed step for the biosynthesis of L‐lysine in bacteria and plants. The enzyme from Escherichia coli is feedback inhibited by lysine, the end product of the pathway. A study of the pH dependence of the kinetic parameters was done to elucidate the acid‐base chemical mechanism of the enzyme. The kinetic mechanism is ping pong with pyruvate binding to free enzyme. The ε‐amino group of lysine 161 attacks the carbonyl of pyruvate and forms a Schiff base intermediate. The loss of a proton from this intermediate leads to the formation of an enamine intermediate, with the loss of the proton accounting for the irreversible step and the ping pong kinetic mechanism. ASA binds to the enzyme:enamine covalent intermediate. Site‐directed mutagenesis was done to investigate the role of the active site arginine 138. The R138A and R138K mutants were created and the identity of the mutants was confirmed. Kinetic studies will be done to characterize the mutant enzymes.This work was supported by grant P20RR016478 from the National Center for Research Resources a component of the National Institutes of Health and a grant from the University of Central Oklahoma office of Research and Grants to L.C.

Approximate Analytical Expressions for the Steady‐State Concentration of Substrate and Cosubstrate over Amperometric Biosensors for Different Enzyme Kinetics

ABSTRACTMathematical models of amperometric biosensors at three basic types of enzyme kinetics in nonstationary diffusion conditions are discussed. The models are based on nonstationary diffusion equations containing a linear term related to the first‐order and nonlinear term related to the Michaelis–Menten and ping–pong of the enzymatic reaction mechanism. In this paper, we obtain approximate closed‐form analytical solutions for the nonlinear equations under steady‐state condition by using the homotopy analysis method. Analytical expressions for concentrations of substrate and cosubstrate and corresponding current response have been derived for all possible values of parameters. Furthermore, in this work, the numerical simulation of the problem is also reported using Scilab/MATLAB program. An agreement between analytical and numerical results is noted.

Non-linear kinetic modelling of reversible bioconversions: Application to the transaminase catalyzed synthesis of chiral amino-alcohols

This work describes the establishment of a full kinetic model, including values of apparent kinetic parameters, for the whole cell E. coli mediated synthesis of the chiral amino-alcohol (2S,3R)-2-amino-1,3,4-butanetriol (ABT), using (S)-(−)-α-methylbenzylamine (MBA) as amino donor. The whole cell biocatalyst expressed the CV2025 ω-transaminase from Chromobacterium violaceum. Establishment of the most suitable reaction mechanism and determination of the complete forward and reverse kinetic parameter values for the reversible bioconversion where obtained using a hybrid methodology. This combined traditional initial rate experiments to identify a solution in the vicinity of the global minimum, with nonlinear regression methods to determine the exact location of the solution. The systematic procedure included selection and statistical evaluation of different kinetic models that best described the measured reaction rates and which ultimately provided new insights into the reaction mechanism; in particular the possible formation of a dead end complex between the amino donor and the cofactor enzyme complex. The hybrid methodology was combined with a microscale experimental platform, to significantly reduce both the number of experiments required as well as the time and material required for full kinetic parameter estimation. The equilibrium constant was determined to be 849, and the forward and reverse rate constants were found to be 97 and 13min−1, respectively, which greatly favoured the asymmetric synthesis of chiral ABT. Using the established kinetic model, the asymmetric synthesis of ABT was simulated, and excellent agreement was found between the experimental and predicted data over a range of reaction conditions. A sensitivity analysis combined with various simulations suggested the crucial bottleneck of the reaction was the second half reaction of the ping pong bi–bi mechanism, in part due to the low Michaelis constant of substrate l-erythrulose (ERY). The toxicity of MBA towards the transaminase was identified as another major bottleneck. The kinetic model was useful to give early insights into the most appropriate bioconversion conditions, which can improve the rate and yield of ABT formation, as well as minimizing the toxicity and inhibition effects of the substrates and products. The systematic methodology developed here is considered to be generic and useful in regard to speeding up bioconversion process design and optimization.

Distribution nucleation: Quantifying liquid distribution on the particle surface using the dimensionless particle coating number

Control of nucleation in wet granulation often determines the size and structure of the final granules. After a decade of research, our knowledge of “immersion nucleation”, where a large droplet engulfs fine particles, is relatively well established. However, far less is known about the second mechanism called “distribution nucleation”, where the powder particles are gradually coated by a layer of small droplets. In this paper, the similarities between particle coating and granulation were used to define the five steps of distribution nucleation. A Bernoulli model was developed to describe the fractional surface coating F, and a new dimensionless parameter, the particle coating number Φp, was defined as the ratio of the theoretical area coated by the drops, assuming no overlap, to the total surface area of the particle.The particle coating number was experimentally validated by adding drops randomly over the surface of a particle and measuring the fractional surface coating using image analysis. Standard ping pong balls (40mm diameter) plus four sizes of foam balls ranging from 20 to 50mm diameter were coated with either small or large drops of melted PEG1000. The results demonstrated that the particle coating number Φp can be used to predict the fractional surface coverage F using simple, known parameters (without any fitting coefficients), and was able to account for differences in particle size and drop size. Deviations in the experimental data from the theoretical predictions were observed, and attributed to drop spreading and merging and heat conduction into the particle, which all affect the experimental drop footprint area. When the effective footprint area was used as a fitting parameter all the experimental data collapsed onto a single line, demonstrating that the particle coating number captures the key coating coverage behaviour.The particle coating number can also be used to predict the effect of changing particle size, surface area, liquid level, or drop size on the coating fraction, which is in turn known to be linked to granulation kinetics. The particle coating number opens up new options for granulation process control, and is expected to be valuable in a variety of particle wetting and coating applications where small drops are distributed over larger particles.

Ping pong fracture in the newborn: illustration of a case

Ping pong fracture in the newborn: illustration of a case

Kinetic model of lipase-catalyzed conversion of ascorbic acid and oleic acid to liposoluble vitamin C ester

The kinetics of l-ascorbyl oleate synthesis catalyzed by immobilized lipase from Candida antarctica in acetone was investigated. Significant inhibition of synthesis with an excess of ascorbic acid was observed. Experimental data were successfully fitted with a ping–pong bi–bi kinetic model with substrate inhibition, and related kinetic constants were determined. The kinetic study was performed at optimum experimental factors (temperature, initial water content, and enzyme concentration), which were determined using response surface methodology. Then, a model for predicting product–time progress curves was developed by expanding the obtained ping–pong model with terms describing ester hydrolysis. Kinetic constants of the reverse reaction were determined, and good congruence between the model and experimental data was achieved. Calculated kinetic constants revealed that lipase has the highest affinity for ascorbyl oleate, slightly lower activity with ascorbic acid, and the lowest activity with oleic acid. The obtained results are valuable for elucidating the reaction mechanism and represent an important contribution for reaction optimization and creating strategies to increase the productivity of vitamin C ester synthesis.

A comprehensive approach to vertical handoff in heterogeneous wireless networks

A multi-criteria vertical handoff system sensitive to various mobile-terminals’ mobility parameters including distance and velocity in a heterogeneous wireless network is analytically formulated and validated via simulations. It is targeted to estimate the essential handoff parameters including outage probability, residual capacity, and signal to interference and noise threshold as well as network access cost. In order to avoid the ping–pong effect in handoff, a signal evolution prediction system is formulated and its performance is examined. Moreover, the handoff scheme is triggered using an on line handoff-initiation-time estimation scheme. When initiated, the handoff procedure begins with a network scoring system based on multi-attribute strategy which results in selection of potentially promising network parameters. Simulation results are shown to track well the analytical formulations.

Sustainability and the Fixed Bed Nuclear Reactor (FBNR)

Sustainability as a multifaceted and holistic concept is analyzed. Sustainability involves human relationship with elements such as natural environment, economy, power, governance, education and technology with the ultimate purpose of carrying forward an ever-advancing civilization. The Fixed Bed Nuclear Reactor (FBNR) is an innovative, small, simple in design, inherently safe, non-proliferating, and environmentally friendly concept that its deployment can generate energy in a sustainable manner contributing to the prosperity of humanity. The development of FBNR will provide electricity as well as desalinated water through a simple but advanced technology for the developing, as well as developed countries. FBNR is environmentally friendly due to its inherent safety and the convenience of using its spent fuel as the source of radiation for irradiation purposes in agriculture, industry, and medicine. Politically, if a ping pong game brought peace between China and USA, a program of development of FBNR supported by the peace loving international community can become a more mature means to bring peace among certain apparently hostile nations who crave sustainable energy, desalinated water and simple advanced technology.

DETERMINING THE TECHNICAL STANDARDS OF PING PONG TABLE BY USING CLOSE RANGE PHOTOGRAMMETRY

Abstract. In the presented study, quality measurements were made regarding three different ping pong tables that were produced with three different materials. Measurements were made on the purpose of confirming whether the tables can be used as a match table that is in the standard of International Table Tennis Federation or not. For this confirmation, bouncing height of the table tennis ball is measured which is approved by ITTF. Average bouncing height that is required by federation standards is minimum 23 cm for free falling table tennis ball from 30 cm. In order to locate the bounce on the tables, the table tennis ball is released from 30cm in free fall with equipment was. In the meantime, 24 video frames videos were shot with a Full HD (1920 × 1080) camera. Each frame of videos that were taken is separated from each other. Each frame is analyzed and highest bounce is measured. As a result of the study, the bouncing heights of the three tables were measured as 23.04 cm, 23.33 cm, 22.91 cm for table1, for table2 and for table3 respectively.

Adaptive Robot Soccer Defence Strategy via Behavioural Trail

Robot soccer is a challenging platform for multi-agent research, involving topics such as real-time image processing and control. A team of robots must work together to put the ball in the opponent’s goal while at the same time defending their own goal. A good strategy for the robot defenders can determine who wins the robotic soccer game. Therefore, the goal of this study is to propose a strategy for the defenders using a production rule based on state diagrams. The rule can facilitate easy and rapid comprehension of certain behaviors with respect to two indicators, such as condition and action. The authors determine five key aspects as conditions, including the positions of two defender robots, the position of the goalkeeper and the ball, and coordination between two defender robots and the goalkeeper robot. Each robot has been set its own defence area and specific actions. They conducted three experiments namely simulator testing, real time testing, and ping pong testing to evaluate their proposed defence strategy. The experimental results show that the authors’ proposed strategy versus three state of the art strategies can defeat up to 92% of all types of attack modes. Meanwhile, in the ping pong testing, their proposed strategy can still protect any goal entering from different attacking modes even though only one or two robots are active in the defence area.

Dynamic Inter Arrival Time Based Seamless Handoff for Mobile WIMAX Ping-Pong Calls Bypassing PKMv2 EAP Authentication

The rapid growth of wireless communication and its persistent use influences all walks of life. Mobile WiMAX IEEE 802.16e standard enabled convergence of mobile and fixed broadband networks through a common wide-area radio-access technology and flexible network architecture. It aims to provide seamless support to its users but an inevitable is that the long delay which occurs during the handoff management in every network process. This paper proposes a Dynamic Interval based Processing Algorithm to separate ping-pong users from the pool of users and to process them separately thus reducing the overhead of network re-entry process. Incoming users are divided into three categories like new user, old user and ping pong user. New user should undergo all the phases of network entry process, old user is provided with authentication key which leads to skipping of steps in generation of keys. Proposed algorithm deals with identifying the ping pong users by calculating the inter arrival duration and rate with same base station. When assured authenticated ping-pong users enter the network next time within the allotted time they will be provided with last used Traffic Encryption Key (TEK) thus bypassing key generation phase . It is observed that the proposed work performs the authentication phase and cancels the key generation phase which leads to minimum network entry delay and it saves to the maximum of 80% processing time. The network model was developed using Network Simulator and the algorithm was implemented in MATLAB GUIDE which gets connected to the database developed in MYSQL.This approach is justified through its timing analysis result which proves the efficient swift in the handoff processes.

Dynamics of some piecewise smooth Fermi-Ulam models

We find a normal form which describes the high energy dynamics of a class of piecewise smooth Fermi-Ulam ping pong models. Depending on the value of a single real parameter, the dynamics can be either hyperbolic or elliptic. In the first case, we prove that the set of orbits undergoing Fermi acceleration has zero measure but full Hausdorff dimension. We also show that for almost every orbit, the energy eventually falls below a fixed threshold. In the second case, we prove that, generically, we have stable periodic orbits for arbitrarily high energies and that the set of Fermi accelerating orbits may have infinite measure.

Lipase catalyzed kinetic resolution of (±)-1-(1-naphthyl) ethanol under microwave irradiation

Abstract 1-(1-Naphthyl) ethanol is an important chiral building block for the synthesis of active pharmaceutical intermediates (APIs). In this work, lipase catalyzed kinetic resolution of ( RS )-1-(1-naphthyl) ethanol via transesterification was studied under microwave irradiation with different acyl donors. Vinyl acetate was the most effective and hence used as the acyl donor. Three different commercially available immobilized lipases were used, among which Candida antarctica lipase B, immobilized on acrylic resin (Novozym 435) was found to be the best catalyst in n-heptane as solvent. The effect of various parameters was studied in a systematic manner. The reaction was intrinsically kinetically controlled. Maximum conversion of 47.74% with enantiometric excess of substrate ( ee s ) of 90.05% and enantiomeric ratio ( E ) of 433.39 was obtained in 3 h using 30 mg of enzyme loading with equi-molar ratio of alcohol to ester at 60 °C. From the progress curve analysis, the ping–pong bi–bi mechanism with inhibition by both substrates was found to fit the initial rates. Kinetic parameters were obtained by using non-linear regression. The process is efficient and easily scalable as compared to the chemical process.