A new multi-wavelength model-based method for determination of enzyme kinetic parameters

Lineweaver-Burk plot analysis is the most widely used method to determine enzyme kinetic parameters. In the spectrophotometric determination of enzyme activity using the Lineweaver-Burk plot, it is necessary to find a wavelength at which only the substrate or the product has absorbance without any spectroscopic interference of the other reaction components. Moreover, in this method, different initial concentrations of the substrate should be used to obtain the initial velocities required for Lineweaver-Burk plot analysis. In the present work, a multi-wavelength model-based method has been developed and validated to determine Michaelis-Menten constants for some enzyme reactions. In this method, a selective wavelength region and several experiments with different initial concentrations of the substrate are not required. The absorbance data of the kinetic assays are fitted by non-linear regression coupled to the numeric integration of the related differential equation. To indicate the applicability of the proposed method, the Michaelis-Menten constants for the oxidation of phenanthridine, 6-deoxypenciclovir and xanthine by molybdenum hydroxylases were determined using only a single initial concentration of the substrate, regardless of any spectral overlap.     

Mathematical modeling of the course and prognosis of factitious disorders: a game-theoretic approach

A mathematical model using simple concepts of repeated games is proposed to model the course and prognosis of factitious disorders. Although simple, the model seems capable of explaining the yet unknown mechanisms underlying the variable course of factitious disorders. One of the notable results of this study is the significant effect of involved physicians in the treatment process on the course of the disease. Particularly, the doctor's error rate in realizing whether the symptoms are real or factitious can considerably affect the course of the disease. This is the first paper to apply a mathematical model to factitious disorders.     

Middle Permian calcareous algae and microproblematica (Dalan Formation, Dena Mountain, High Zagros, SW Iran)

Calcareous algae and microproblematica have been studied in the Middle Permian part of the Dalan Formation in Dena Mountain, Zagros, southwest Iran. Murgabian (=Wordian) microfossils are the most diversified. The assemblages encompass, among the dasycladales, Anthracoporella spectabilis, Epimastopora piae, Epimastoporella japonica, E. likana, Paraepimastopora? cf. densipora n. comb., Gyroporella cf. nipponica, G.? aff. fluegeli n. comb., G.? aff. symmetrica, G.? aff. digitula n. comb., Mizzia yabei; among the gymnocodiaceans, Gymnocodium bellerophontis, G. nodosum, Permocalculus cf. digitatus, P. forcepinus, P. cf. fragilis, P. plumosus, P. cf. solidus, Tauridium? sp.; among the “phylloid algae” Eugonophyllum? sp.; among the other incertae sedis algae Stacheoides sp., Ungdarella uralica, Fourstonella (Efluegelia) johnsoni, and among some microproblematica alternatively assigned to foraminifers or algae Aeolisaccus dunningtoni, Tubiphytes obscurus, Pseudovermiporella nipponica, P. sodalica, and P. longipora. Each taxon is briefly characterized, whereas a more detailed analysis of the epimastoporacean algae is given. Among them, the genera Epimastopora and Epimastoporella are emended. All the described microfossils have a relatively broad stratigraphic distribution in the Permian period but they are paleoecologically important. They are indeed confident micropaleontological Middle Permian proxies, particularly for shallow-marine, warm, well-oxygenated and relatively high-energy environments. They were affected by the end-Guadalupian crisis because they strongly decrease in the upper carbonate unit of the Dalan Formation and are not found in the Triassic sediments of the area.     

Interferon-Gamma Increases the Ratio of Matrix Metalloproteinase-9/Tissue Inhibitor of Metalloproteinase-1 in Peripheral Monocytes from Patients with Coronary Artery Disease

Acute coronary syndromes (ACS) may be triggered by acute infections. Systemic production of interferon gamma (IFN-γ) is induced during infection and regulates the production of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs), both important in plaque stability. This study evaluates the effect of IFN-γ on the MMPs/TIMP-1 ratio in cultured monocytes from 30 patients with stable coronary artery disease (CAD), 30 with unstable angina (UA) or non-ST-segment elevation myocardial infarction (NSTEMI), and 30 healthy blood donors. Supernatant concentrations of MMP-1, -2, -9, and TIMP-1 were measured by enzyme-linked immunoassays. Basal concentration of MMP-1 and TIMP-1 was similar between groups, while MMP-2 was higher in healthy individuals and MMP-9 in patients with UA/NSTEMI. Upon IFN-γ stimulation, MMP-9 secretion increased in all groups, while TIMP-1 decreased only in patients with CAD, which in turn result in a strikingly elevation in their mean MMP-9/TIMP-1 ratio. MMP-1/TIMP-1 and MMP-2/TIMP-1 ratios were <1.0 in basal conditions and after stimulation in all groups. Our results suggest that nonstimulated monocytes from patients with stable CAD show a similar behavior than those from healthy individuals. However, stimulation with IFN-γ induces an increase on the MMP-9/TIMP-1 ratio as high as that found in patients with ACS. Thus, it may bring biological plausibility to the association between acute infections and the development of ACS.     

Unraveling the iron deficiency responsive proteome in <i>Arabidopsis?</i>shoot by iTRAQ-OFFGEL approach

Iron (Fe) is required by plants for basic redox reactions in photosynthesis and respiration, and for many other key enzymatic reactions in biological processes. Fe homeostatic mechanisms have evolved in plants to enable the uptake and sequestration of Fe in cells. To elucidate the network of proteins that regulate Fe homeostasis and transport, we optimized the iTRAQ-OFFGEL method to identify and quantify the number of proteins that respond to Fe deficiency in the model plant Arabidopsis. In this study, Fe deficiency was created using Fe-deficient growth conditions, excess zinc (Zn), and use of the irt1-1 mutant in which the IRT1 Fe transporter is disrupted. Using the iTRAQ-OFFGEL approach, we identified 1139 proteins, including novel Fe deficiency-responsive proteins, in microsomal fractions isolated from 3 different types of Fe-deficient shoots compared with just 233 proteins identified using conventional iTRAQ-CEX. Further analysis showed that greater numbers of low-abundance proteins could be identified using the iTRAQ-OFFGEL method and that proteins could be identified from numerous cellular compartments. The improved iTRAQ-OFFGEL method used in this study provided an efficient means for identifying greater numbers of proteins from microsomal fractions of Arabidopsis shoots. The proteome identified in this study provides new insight into the regulatory cross talk between Fe-deficient and excess Zn conditions.     

Double Diffusive Magnetohydrodynamic (MHD) Mixed Convective Slip Flow along a Radiating Moving Vertical Flat Plate with Convective Boundary Condition

In this study combined heat and mass transfer by mixed convective flow along a moving vertical flat plate with hydrodynamic slip and thermal convective boundary condition is investigated. Using similarity variables, the governing nonlinear partial differential equations are converted into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved using a semi-numerical/analytical method called the differential transform method and results are compared with numerical results. Close agreement is found between the present method and the numerical method. Effects of the controlling parameters, including convective heat transfer, magnetic field, buoyancy ratio, hydrodynamic slip, mixed convective, Prandtl number and Schmidt number are investigated on the dimensionless velocity, temperature and concentration profiles. In addition effects of different parameters on the skin friction factor, , local Nusselt number, , and local Sherwood number are shown and explained through tables.     

The different patterns of post-heat stress responses in wheat genotypes: the role of the transthylakoid proton gradient in efficient recovery of leaf photosynthetic capacity

Photosynthesis Research - The frequency and severity of heat waves are expected to increase in the near future, with a significant impact on physiological functions and yield of crop plants. In...     

Photosynthesis research under climate change

Increasing global population and climate change uncertainties have compelled increased photosynthetic efficiency and yields to ensure food security over the coming decades. Potentially, genetic manipulation and minimization of carbon or energy losses can be ideal to boost photosynthetic efficiency or crop productivity. Despite significant efforts, limited success has been achieved. There is a need for thorough improvement in key photosynthetic limiting factors, such as stomatal conductance, mesophyll conductance, biochemical capacity combined with Rubisco, the Calvin–Benson cycle, thylakoid membrane electron transport, nonphotochemical quenching, and carbon metabolism or fixation pathways. In addition, the mechanistic basis for the enhancement in photosynthetic adaptation to environmental variables such as light intensity, temperature and elevated CO₂ requires further investigation. This review sheds light on strategies to improve plant photosynthesis by targeting these intrinsic photosynthetic limitations and external environmental factors.