Although there is enough knowledge indicating on the influence of frequency content of input motion on the deformation demand of structures, state-of-the-practice seismic studies use the intensity measures such as peak ground acceleration (PGA) which are not frequency dependent. The VMAX/amax  ratio of strong ground motions can be used in seismic hazard studies as the representative of frequency content of the motions. This ratio can be indirectly estimated by the attenuation models of PGA and PGV which are functions of earthquake magnitude, source to site distance, faulting mechanism, and local site conditions. This paper presents new predictive equations for VMAX/amax ratio based on genetic programming (GP) approach. The predictive equations are established using a reliable database released by Pacific Earthquake Engineering Research Center (PEER) for three types of faulting mechanisms including strikeslip, normal and reverse. The proposed models provide reasonable accuracy to estimate the frequency content of site ground motions in practical projects. The results of parametric study demonstrate that VMAX/amax increases through increasing earthquake moment magnitude and source to site distance while it decreases with increasing the average shear-wave velocity over the top 30m of the site.

Background: Phenytoin is commonly administered as an anticonvulsant agent to critically traumatic patients for seizure prophylaxis and treatment. It exhibits non-linear pharmacokinetic characteristic and requires frequent plasma level monitoring and dose adjustment. Based on the previous study, it is often difficult to achieve therapeutic levels in patients with head trauma using the recommended phenytoin dosing strategies. Therefore, we conducted a prospective, randomized study to evaluate pharmacokinetic parameters of phenytoin in patients with head trauma.Materials and methods: In this prospective randomized study, eighty-three patients were enrolled. The dosing regimen of phenytoin was designed and individualized for each patient based on available population pharmacokinetic data and was compared with the administered dose. The peak and trough concentrations of collected blood samples were determined by TDX.Results: Statistical analysis of the findings indicated that there were significant differences between administered doses of phenytoin and calculated doses based on peak and trough (P<0.0001). Additonally, our findings indicate the significant difference between previous population VMAX and VMAX obtain from this study. Furthermore, this study showed that phenytoin plasma concentrations were sub therapeutic in the majority of cases (71 %).Conclusions: It seems that blood level monitoring of phenytoin in patients with neurosurgical trauma on the basis of drug pharmacokinetic parameters such as VMAX is necessary.

Polyphenol oxidase (PPO) was extracted from three segments of Solanum melongenas and Musa sapietum fruits and partially purified. The specific activity of PPO was measured at each purification step to ascertain level of enzyme purity. In all cases, PPO conformed to Michaelis-Menten kinetics, showing different values of kinetics parameters. Michaelis-Menten constant (PPOKm) of S. melongenas mid-section and anterior segments showed no significant difference (p<0.05), whereas the posterior gave PPOKm=4.6±0.49 mM (p>0.05). Maximum PPO activity (PPOVMAX) was highest in the posterior segment: PPOVMAX=0.602±0.09 U. Mid-section of M. sapietum exhibited the highest Km value (PPOKm=5.8±0.69 mM) compared with the anterior (PPOKm=3.9±0.69 mM) (p>0.05) and posterior PPOKm=4.9±0.11 mM segments (p<0.05). Overall, M. sapietum PPOKm values were relatively higher than those of S. melongenas. Posterior S. melongenas exhibited the highest PPOVMAX=0.602±0.09 U, whereas the lowest value was registered in the anterior segment of M. sapietum PPOVMAX=0.234±0.09 U. Substrate specificity for PPO (PPOVMAX/Km) extracted from various segments of S. melongenas was in the increasing order of Mid-section>Posterior>Anterior, whereas that of M. sapietum was Mid-section>Anterior>Posterior. PPOVMAX/Km between the two fruits showed strong positive correlation (r=0.862339). Catechol was a better substrate for PPOS. melongenas than PPOM. sapietum. The experimentally observed kinetic parameters of S. melongenas and M. sapietum signified the presence of PPO isoenzymes and non-uniform distribution of PPO in the two fruits.

Alpha-amylase is one of the most widely used enzymes in the starch industry. However, industrial application of soluble alpha-amylase is hampered by changes in pH and temperature (adverse effects on enzyme stability) and activity loss, leading to higher costs. Immobilization of alphaamylase is an efficient strategy to reduce the enzyme losing and subsequently reduces costs in this regard. Alpha-amylases are immobilized by adsorption, entrapment, covalent attachment, and cross-linking. A barrier in alpha-amylase immobilization is the large size of its substrate, namely amylose and amylopectin. Most of these immobilization methods decrease the affinity of the enzyme for its substrate as well as the maximum rate of reaction (VMAX). This review aims to study different aspects of alpha-amylase including enzyme activity, applications, structure, starch, immobilization methods, and immobilization’, s obstacles to improve alpha-amylase efficiency in the industry and also lowering the costs related to providing this enzyme.

Root influx parameters (VMAX and Km) of wheat (Triticum aestivum var. HD-2285) were determined at different stages of crop growth, viz. CRIS-Crown Root Initiation Stage, MTS-Maximum Tillering Stage, FLS-Flag Leaf Stage and DFS-Dough Formation Stage. Wheat was grown in sand medium with Hoagland nutrient solution (all nutrients except potassium). Plants were taken out from sand culture at 22, 41, 69, and 87 days after germination (DAG) and placed in a specially designed assembly of flowing solution in laboratory and greenhouse. The nutrient solution allowed to flow into the culture vessel in a regulated manner by means of a separating funnel. Fresh Hoagland solutions having five different concentration of K+ (0.051, 0.154, 0.256, 0.333, and 0.410 mM) were added drop-wise on the funnels at the rate of about 35 mL s-1 and continuously supplied in five different assemblies. Root influx parameters (VMAX and Km) were determined employing a simple solution culture technique, by measuring the depletion of potassium (input-output concentration) by wheat roots in five nutrient media differing in potassium concentration only. VMAX and Km were calculated with the help of coefficients obtained by fitting the solution K+ concentration and K+ uptake rate data on the Michaelis-Menten equation. The VMAX and Km values were decreased with the age of wheat crop. The VMAX was 48.7 nmol m-2 s-1 at 22 DAG and decreased to 19.4 nmol m-2 s-1 at 41 DAG, 5.90 nmol m-2 s-1 at 69 DAG and finally decreased to 4.21 nmo1m-2 s-1 at 87 days of crop growth; corresponding Km values were 0.299, 0.254, 0.176 and 0.146 mM, respectively.

Dear Editor, Years of experience in teaching biochemistry and enzymology courses, especially the discussion of enzyme kinetics, has enabled us to determine the kinetic parameters of enzymes, especially the Michaelis constant Km and the maximum reaction speed VMAX using various mathematical equations. These equations include the Michaelis-Menten equation and many of its linear derivatives such as Lineweaver-Burk, Woolf-Augustinsson-Hofstee (EadieHofstee in some text books), Eadie-Scatchard, and HanesWoolf equations (1, 2). However, it seems that none of the above linear graphs can directly and quickly calculate the kinetic parameters of the Michaelis constant Km and the maximum reaction speed VMAX from the line equation. This inspired us to think about a new linear derivative of the Michaelis-Menten equation, by which we can directly calculate the Michaelis constant Km and the maximum reaction rate VMAX from the equation of the graph line.

Positive ventilation has shown to have an influence on pharmacokinetic and disposition of some drugs. Beacause phenytoin with a narrow therapautic range, is the most commonly used drug for prophylaxis and treatment of early seizures after acute brain injuries, in the present study the effect of short term PEEP (5-10 cm H2O for at least 8 hours) on phenytoin serum concentration and pharmacokinetic parameters such as VMAX and clearance in brain injured patients under mechanical ventilation was examined. Ten patients with moderate to severe acute brain injury who were placed on mechanical ventilation with an initial PEEP level of 0-5 cm H2O were included in the study. Patients received phenytoin loading dose of 15 mg/kg followed by a maintenance daily dose of 3-7 mg/kg initiated within 12 hours of loading dose. Sampels were taken on two different occasions before and after PEEP elevation. Total phenytoin serum concentrations were determined by HPLC method. A time invarient Michaelis-Menten pharmacokinetic model was used to calculate VMAX and clearance for each patient. Derrived variables were calculated as follows: VMAX, 3.5-6.8 and 3.7-8.2 mg/kg/day; Clearance, 0.1-0.7 and 0.1-1.2 l/kg/day (before and after PEEP elevation, respectively). Our data have shown a wide range of variability (2.6-32.5 mg/l) in phenytoin serum concentrations. There were no statistically significant differences in the measured total concentrations (p=0.721) and calculated VMAX and clearance (p=0.285) before and after PEEP elevation. Administration of fluid and inotropic agents, limitation in application of higher levels of PEEP and drug interactions, shall be considered as possible explanations for these findings.