There are a variety of methods available to calculate the inhibition constant (Ki) that characterizes substrate inhibition by a competitive inhibitor. Linearized versions of the Michaelis-Menten equation (e.g., Lineweaver-Burk, Dixon, etc.) are frequently used, but they often produce substantial errors in parameter estimation. This study was conducted to compare three methods of analysis for th...

250 words Introduction: 701 words Discussion: 1500 words Abbreviations used are: DDI, drug-drug interaction; HLM, human liver microsomes; fuinc, fraction unbound in incubation; MBI, mechanism-based inhibition; MIC, metabolite intermediate complex; Km, Michaelis-Menten constant; kinact, inactivation rate constant; KI, irreversible inhibition constant; Ki, reversible inhibition constant. This art...

the main objective of this study was to purify and characterize an esterase from shewanella sp f88. the enzyme was purified 41-fold and an overall yield of 21 %, using a two-step procedure, including ammonium sulfate precipitation and q-sepharore chromatography. molecular weight of the enzyme was 62.3 kda according to sds-page data. the enzyme showed an optimum activity at ph 6.5 and 58 ˚c. evo...

where E denotes a molecule of the enzyme phosphodiesterase (PDE), X1 denotes a molecule of c-di-GMP and P is the product of this reaction, pGpG. Here, we made a quasi steady-state assumption for the formation of the E:X1-complex. This makes the product formation the rate limiting step, yielding the maximal catalytic velocity Vmax = (e + ex1) · k cat and the Michaelis-Menten constant Km = (k PDE...

For enzymatic progress curves conforming to the Michaelis–Menten mechanism (E + S ES → E + P) under the experimental conditions where the substrate concentration is at least several times smaller than the Michaelis constant, the minimal fitting model cast as a system of numerically integrated differential equations is the simple ‘hit-and-run’ mechanism, E + S → E + P. The best-fit value of sing...

Polyphenol oxidase (PPO) from tomatoes was extracted and partially purified through  (NH4)2SO4 precipitation, dialysis and ion exchange chromatography. The activity of polyphenol oxidase was investigated in solanum lycopersicum. Spectrophotometric method was used to assay the enzyme activity and the kinetic constants - maximum enzyme velocity (Vmax) and Michealis - Menten constant (Km). Of the ...

The purposes of this paper are (a) to examine the effect of calorimeter time constant (τ) on heat rate data from a single enzyme injection into substrate in an isothermal titration calorimeter (ITC), (b) to provide information that can be used to predict the optimum experimental conditions for determining the rate constant (k2), Michaelis constant (KM), and enthalpy change of the reaction (ΔRH)...

polyphenol oxidase (ppo) from tomatoes was extracted and partially purified through  (nh4)2so4 precipitation, dialysis and ion exchange chromatography. the activity of polyphenol oxidase was investigated in solanum lycopersicum. spectrophotometric method was used to assay the enzyme activity and the kinetic constants - maximum enzyme velocity (vmax) and michealis - menten constant (km). of the ...

Two steps of enzymatic oxidations from hypoxanthine to uric acid with xanthine oxidase (XOD) were kinetically analyzed by capillary electrophoresis/dynamic frontal analysis. When a substrate solution was introduced into separation buffer containing XOD, the reaction continuously proceeded during electrophoresis and product resolved zone. A plateau signal detected based on constant rate XOD. The...

We demonstrate the versatility of Al2O3-passivated Si nanowire devices ("nanoribbons") in the analysis of enzyme-substrate interactions via the monitoring of pH change. Our approach is shown to be effective through the detection of urea in phosphate buffered saline (PBS), and penicillinase in PBS and urine, at limits of detection of <200 μM and 0.02 units/mL, respectively. The ability to extrac...