In this paper the nature and validity of the mathematical formulation of MichaelisMenten type kinetics for enzyme-catalysed biochemical reactions is studied. Previous work has in the main concentrated on isolated, spatially uniform (well-mixed) reactions. We investigate the effects of substrate input and diffusion on this formulation, in particular, on the nature and validity of the quasi-stead...

Strains of German cockroach, Blattella germanica (L.) were tested for resistance to three insecticides using the time-mortality response technique in comparison with known susceptible strains. Dursban-R and Macy strains indicated high levels of resistance to chlorpyrifos and moderate resistance to propoxur and cypermethrin. The hydrolytic activity of esterase enzymes was determined with a model...

A fast uptake of the preservative benzoic acid was observed in Saccharomyces cerevisiae, reaching saturation in about two min and then remaining constant at this level. The strong dependence of benzoic acid uptake on pH was due to the relative distribution of molecular and ionic forms in solution and not to the pH itself. The molecular form was the only one taken up by the cells. The specificit...

A novel biosensor was developed by immobilizing hemoglobin (Hb) on a glassy carbon electrode (GCE) modified with a composite of ZnO nano-rods and carbon nanofiber (CNF), a strong reducer, hydrazine, was firstly used to evaluate the electrochemical behavior of Hb on Hb/ZnO/CNF/GCE. UV-vis and circular dichroism (CD) spectra indicated the conformational structure of Hb interaction with ZnO/CNF wa...

A novel impedimetric biosensor was fabricated for total cholesterol sensing based on platinum nanoparticle and polypyrrole multilayer nanocomposite electrode. The Pt nanoparticles (PtNP) electrochemically deposited between two polypyrrole layers on indium tin oxide (ITO) glass plates (PtNP/PPY/ITO) have offered high-electroactive surface area and favourable microenvironment for immobilization o...

The study determined the population estimates for Km and Vmax of phenytoin in Thai patients. The serum phenytoin concentrations collected prospectively from outpatients who received phenytoin were analyzed to estimate population pharmacokinetic parameters. There were 197 steady-state concentrations and associated dosage rates (mg/day) from 167 outpatients. The data were analyzed using NONMEM, a...

Lignocellulosic biomass is a potential source of renewable, low-carbon-footprint liquid fuels. Biomass recalcitrance and enzyme cost are key challenges associated with the large-scale production of cellulosic fuel. Kinetic modeling of enzymatic cellulose digestion has been complicated by the heterogeneous nature of the substrate and by the fact that a true steady state cannot be attained. We pr...

The behavior of individual Na channels in the apical membrane of the rat cortical collecting tubule (CCT) was studied at different concentrations of the permeant ions Na and Li. Tubules were opened to expose their luminal surfaces and bathed in K-gluconate medium to minimize tubule-to-tubule variation in cell membrane potential and intracellular Na concentration. The patch-clamp technique was u...

Rat canalicular membranes contain microdomains enriched in cholesterol and ATP-binding cassette transporters. Cholesterol is known to regulate the activity of transporters. Here, we investigated the effect of membrane cholesterol on the transport kinetics of multidrug resistance-associated protein 2 (MRP2) and of bile salt export pump (BSEP) variants and mutants. MRP2 and BSEP were expressed wi...