Sharif Digital Repository

The kinetics of the enzymic reaction of penicillin G acylase from a mutant of Escherichia coli ATCC 11105 in forward and reverse directions were studied and the kinetic constants determined. Results show that the enzyme is inhibited by excess substrate, penicillin G (Pen G), and by both products. The non-competitive inhibition by 6-aminopenicillanic acid (6-APA) and competitive inhibition by phenylacetic acid were observed for the ordered uni bi deacylation reaction in the forward direction. The optimum pH value for the reverse acylation reaction was 5.7. The bi uni mechanism for the reverse reaction was investigated and the inhibitory effects of the substrates, 6-APA and phenyl acetic acid,... 

Quantitative Structure - Activity Relationship (QSAR) models for the inhibition action of some 1-phenylbenzimidazoles on platelet-derived growth are constructed using Genetic Algorithm and Artificial Neural Network (GA-ANN) method. The statistical parameters of R2 and root-mean-square error are 0.82 and 0.21, respectively using this method. These parameters show a considerable improvement compared to the stepwise multiple linear regression combined with ANN (stepwise MLR-ANN). Ten-fold shuffling crossvalidations are carried out to select the most important descriptors. Five descriptors of index of Balaban (J), average molecular weight (AMW), 3D-Wiener index (W3D), mean atomic van der Waals... 

This paper presents a new method for spectrophotometirc detection of sulfide applying fungal peroxidase immobilized on sodium alginate. The sensing scheme was based on decrease of the absorbance of the orange compound, purpurogallin produced from pyrogallol and H2O2 as substrates, due to the inhibition of peroxidase by sulfide. Absorbance of purpurogallin was detected at 420nm by using a spectrophotometer. The proposed method could successfully detect the sulfide in the concentration range of 0.6-7.0μM with a detection limit of 0.4μM. The kinetic parameters of Michaelis-Menten with and without sulfide were also calculated. Possible inhibition mechanism of peroxidase by sulfide was deduced... 

The effects of temperature, seed mass and agitation rate on agglomeration kinetics of aluminum hydroxide in Bayer process have been studied in a batch system. Collected raw data were analyzed and the kinetics data of agglomeration were derived through simulation of the process using a pre-developed software. The results showed that agglomeration kinetics constant (agglomeration kernel) increases with increase in temperature and agitation rate. Moreover a maximum value of agglomeration rate versus added seed mass was observed. Furthermore the magnitude of calculated activation energy of agglomeration was close to that of growth  

In this study the ability of Acidithiobacillus ferrooxi-dans, with regard to the biorecovery of heavy metals in shake flask has been investigated. Adaptation experiments with the single metal ions Ni, Co, V, Mo, W and a mixture of the first four metal ions in the medium was developed through serial sub-culturing. Adaptation showed that A. ferrooxidans could tolerate up to 2.3 g/l Ni, 1.4 g/l Co, 1.4 g/l V, 0.045 g/l Mo and 0.005 g/l W, singly. In the presence of multi-metals considering a mixture of Ni-Co-V-Mo, the bacteria was able to tolerate up to 1.5 g/l Ni, 0.8 g/l Co, 0.8 g/l V and 0.05 g/l Mo in steps of 50-100 mg/l for Ni, Co and V, while for Mo and W with increments in concentration... 

Conformational diseases, constituting a large number of diseases, have been connected with protein misfolding, leading to aggregation known as amyloid fibrils. Mainly due to the lack of detailed molecular mechanisms, there has not been an effective drug to combat amyloid-associated diseases. Recently, a small organic pyridazine-based molecule (RS-0406) has shown significant reductions in amyloid fibrils in both in vitro and in vivo animal studies. However, no information on molecular details of inhibition for the small molecule has been reported. In this work, we have decided to explore structure-activity relationship of pyridazine-based compounds to investigate structural parameters for...