Saher Khan - Academia.edu (original) (raw)

Papers by Saher Khan

Biochimica Et Biophysica Acta-general Subjects, 1999

An extracellular L-galactosidase from a thermophilic fungus Rhizomucor sp. has been purified to h... more An extracellular L-galactosidase from a thermophilic fungus Rhizomucor sp. has been purified to homogeneity by successive DEAE cellulose chromatography followed by gel filtration on Sephacryl S-300. The native molecular mass of the enzyme is 250 000 and it is composed of two identical subunits with molecular mass of 120 000. It is an acidic protein with a pI of 4.2. Purified L-galactosidase is a glycoprotein and contains 8% neutral sugar. The optimum pH and temperature for enzyme activity are 4.5 and 60³C, respectively. The enzyme is stable at 60³C for 4 h, and has a t 1a2 of 150 min at 70³C which is one of the highest reported for fungal L-galactosidases. Substrate specificity studies indicated that the enzyme is specific for L-linked galactose residues with a preference for p-nitrophenyl-L-D-galactopyranoside (pNPG). The K m and V max values for the synthetic substrates pNPG and o-nitrophenyl-L-D-galactopyranoside (oNPG) were 0.66 mM and 1.32 mM; and 22.4 mmol min 31 mg 31 and 4.45 mmol min 31 mg 31 , respectively, while that for the natural substrate, lactose, was 50.0 mM and 12 mmol min 31 mg 31 . The end product galactose and the substrate analogue isopropyl thiogalactopyranoside (ITPG) inhibited the enzyme with K i of 2.6 mM and 12.0 mM, respectively. The energy of activation for the enzyme using pNPG and oNPG were 27.04 kCal and 9.04 kCal, respectively. The active site characterization studies using group-specific reagents revealed that a tryptophan and lysine residue play an important role in the catalytic activity of the enzyme. ß 1999 Published by Elsevier Science B.V. All rights reserved.

Journal of Industrial Microbiology & Biotechnology, 1997

A thermostable β-galactosidase was produced extracellularly by a thermophilic Rhizomucor sp, with... more A thermostable β-galactosidase was produced extracellularly by a thermophilic Rhizomucor sp, with maximum enzyme activity (0.21 U mg−1) after 4 days under submerged fermentation condition (SmF). Solid state fermentation (SSF) resulted in a nine-fold increase in enzyme activity (2.04 U mg−1). The temperature range for production of the enzyme was 38–55°C with maximum activity at 45°C. The optimum pH and temperature for the partially purified enzyme was 4.5 and 60°C, respectively. The enzyme retained its original activity on incubation at 60°C up to 1 h. Divalent cations like Co2+, Mn2+, Fe2+ and Zn2+ had strong inhibitory effects on the enzyme activity. The K m and V max for p-nitrophenyl-β- D-galactopyranoside and o-nitrophenyl-β - D-galactopyranoside were 0.39 mM, 0.785 mM and 232.1 mmol min−1 mg−1 respectively. The K m and V max for the natural substrate lactose were 66.66 μM and 0.20 μ mol min−1 mg−1.

Journal of Experimental Botany, 2010

Salinity affects normal growth and development of plants depending on their capacity to overcome ... more Salinity affects normal growth and development of plants depending on their capacity to overcome the induced stress. The present study was focused on the response and regulation of the antioxidant defence system in Brassica oleracea roots under short and long salt treatments. The function and the implications of hydrogen peroxide as a stressor or as a signalling molecule were also studied. Two different zones were analysed-the elongation and differentiation zone and the fully differentiated root zone-in order to broaden the knowledge of the different effects of salt stress in root. In general, an accumulation of hydrogen peroxide was observed in both zones at the highest (80 mM NaCl) concentration. A higher accumulation of hydrogen peroxide was observed in the stele of salt-treated roots. At the subcellular level, mitochondria accumulated hydrogen peroxide in salt-treated roots. The results confirm a drastic decrease in the antioxidant enzymes catalase, ascorbate peroxidase, and peroxidases under short salt treatments. However, catalase and peroxidase activities were recovered under long salt stress treatments. The two antioxidant molecules analysed, ascorbate and glutathione, showed a different trend during salt treatments. Ascorbate was progressively accumulated and its redox state maintained, but glutathione was highly accumulated at 24 h of salt treatment, but then its concentration and redox state progressively decreased. Concomitantly, the antioxidant enzymes involved in ascorbate and glutathione regeneration were modified under salt stress treatments. In conclusion, the increase in ascorbate levels and the maintenance of the redox state seem to be critical for root growth and development under salt stress.

The systems are required to understand and present at higher levels of abstractions to perform ch... more The systems are required to understand and present at higher levels of abstractions to perform changes or re-engineer to meet the current requirements. The software systems drift away from the existing implemented source code and the documentations due to the changes. The high level models are used for the purpose of recovering the artifacts and understanding the system to perform the maintenance activities. This paper presents an approach to develop the high level models from the existing source code and documents.

This paper gives an insight into the working and efficiency of the two basic algorithms used for ... more This paper gives an insight into the working and efficiency of the two basic algorithms used for parameter estimation: Ordinary Least Squares (OLS) and Recursive Least Squares (RLS). A simple DC motor is taken here as an example of a SISO system. The input voltage and the output in the form of rotations of the motor are given to the parameter estimator. The parameters of the motor are determined using both the algorithms and, hence, a comparison is given on the basis of those results.

Amino Acids, 2009

Post-translational modifications such as glycosylation are important for changing the properties ... more Post-translational modifications such as glycosylation are important for changing the properties and functions of proteins. To analyze the importance of glycosylation during cold stress in rice, a proteomics approach was used. Proteins extracted from the basal part of rice leaf sheaths were separated by two-dimensional polyacrylamide gel electrophoresis, and subjected to lectin blot analysis using concanavalin A. From a total of 250 detected proteins, 22 reacted with the lectin, suggesting that they were N-glycosylated proteins. To determine how N-glycosylation of these proteins is affected by cold stress, rice seedlings were incubated at 5°C for 48 h, and proteins extracted from the basal parts of leaf sheaths were analyzed by the lectin blot assay. Cold stress changed the reactivity toward the lectin for 12 of the 22 glycoproteins. The identity of the 12 proteins was determined by protein sequencing and mass spectrometry with the majority of these glycoproteins being categorized as involved in energy production. Furthermore, calreticulin, one of the 12 glycoproteins, was also phosphorylated as a result of cold stress. These results indicate that cold stress of the basal parts of rice leaf sheaths changes the glycosylation and phosphorylation profiles of calreticulin, a key protein that regulates the quality control of other proteins.

The systems are required to understand and present at higher levels of abstractions to perform th... more The systems are required to understand and present at higher levels of abstractions to perform the changes and meet the current requirements. When the changes are performed, the source code drifts away from the existing available system documentation (specifications, design, manuals), which represent the functionality of the software systems. The software systems are developed using the multi-languages with different dialects and scripts. This paper presents a clustering approach using the available source code, documentation, experience and knowledge about the domain and application to cluster the source code. The source code clustering is used for the purpose of recovering the artifacts, understanding the system and identifying the relationships among the source code to plan, design and execute the changes in the software systems.

The idea of the absurd is a common theme in many existentialist works. The philosophy that encomp... more The idea of the absurd is a common theme in many existentialist works. The philosophy that encompasses the absurd is referred to as absurdism. While absurdism may be considered a branch of existentialism, it is a specific idea that is not necessary to an existentialist view Absurdism is the conflict of human existence,with the human tendency to look for meaning and value in life and human inability to find any, and will ultimately fail. Existentialism is how human address this conflict, by knowing the lack of objective meaning it is therefore the responsibility of individuals to give their own lives meaning. So absurdism doesn't state that there isn't any meaning, but it is impossible for humans to know it whereas the existentialist explicitly believe there isn't any value at all.

Biochimica Et Biophysica Acta-general Subjects, 1999

An extracellular L-galactosidase from a thermophilic fungus Rhizomucor sp. has been purified to h... more An extracellular L-galactosidase from a thermophilic fungus Rhizomucor sp. has been purified to homogeneity by successive DEAE cellulose chromatography followed by gel filtration on Sephacryl S-300. The native molecular mass of the enzyme is 250 000 and it is composed of two identical subunits with molecular mass of 120 000. It is an acidic protein with a pI of 4.2. Purified L-galactosidase is a glycoprotein and contains 8% neutral sugar. The optimum pH and temperature for enzyme activity are 4.5 and 60³C, respectively. The enzyme is stable at 60³C for 4 h, and has a t 1a2 of 150 min at 70³C which is one of the highest reported for fungal L-galactosidases. Substrate specificity studies indicated that the enzyme is specific for L-linked galactose residues with a preference for p-nitrophenyl-L-D-galactopyranoside (pNPG). The K m and V max values for the synthetic substrates pNPG and o-nitrophenyl-L-D-galactopyranoside (oNPG) were 0.66 mM and 1.32 mM; and 22.4 mmol min 31 mg 31 and 4.45 mmol min 31 mg 31 , respectively, while that for the natural substrate, lactose, was 50.0 mM and 12 mmol min 31 mg 31 . The end product galactose and the substrate analogue isopropyl thiogalactopyranoside (ITPG) inhibited the enzyme with K i of 2.6 mM and 12.0 mM, respectively. The energy of activation for the enzyme using pNPG and oNPG were 27.04 kCal and 9.04 kCal, respectively. The active site characterization studies using group-specific reagents revealed that a tryptophan and lysine residue play an important role in the catalytic activity of the enzyme. ß 1999 Published by Elsevier Science B.V. All rights reserved.

Journal of Industrial Microbiology & Biotechnology, 1997

A thermostable β-galactosidase was produced extracellularly by a thermophilic Rhizomucor sp, with... more A thermostable β-galactosidase was produced extracellularly by a thermophilic Rhizomucor sp, with maximum enzyme activity (0.21 U mg−1) after 4 days under submerged fermentation condition (SmF). Solid state fermentation (SSF) resulted in a nine-fold increase in enzyme activity (2.04 U mg−1). The temperature range for production of the enzyme was 38–55°C with maximum activity at 45°C. The optimum pH and temperature for the partially purified enzyme was 4.5 and 60°C, respectively. The enzyme retained its original activity on incubation at 60°C up to 1 h. Divalent cations like Co2+, Mn2+, Fe2+ and Zn2+ had strong inhibitory effects on the enzyme activity. The K m and V max for p-nitrophenyl-β- D-galactopyranoside and o-nitrophenyl-β - D-galactopyranoside were 0.39 mM, 0.785 mM and 232.1 mmol min−1 mg−1 respectively. The K m and V max for the natural substrate lactose were 66.66 μM and 0.20 μ mol min−1 mg−1.

Journal of Experimental Botany, 2010

Salinity affects normal growth and development of plants depending on their capacity to overcome ... more Salinity affects normal growth and development of plants depending on their capacity to overcome the induced stress. The present study was focused on the response and regulation of the antioxidant defence system in Brassica oleracea roots under short and long salt treatments. The function and the implications of hydrogen peroxide as a stressor or as a signalling molecule were also studied. Two different zones were analysed-the elongation and differentiation zone and the fully differentiated root zone-in order to broaden the knowledge of the different effects of salt stress in root. In general, an accumulation of hydrogen peroxide was observed in both zones at the highest (80 mM NaCl) concentration. A higher accumulation of hydrogen peroxide was observed in the stele of salt-treated roots. At the subcellular level, mitochondria accumulated hydrogen peroxide in salt-treated roots. The results confirm a drastic decrease in the antioxidant enzymes catalase, ascorbate peroxidase, and peroxidases under short salt treatments. However, catalase and peroxidase activities were recovered under long salt stress treatments. The two antioxidant molecules analysed, ascorbate and glutathione, showed a different trend during salt treatments. Ascorbate was progressively accumulated and its redox state maintained, but glutathione was highly accumulated at 24 h of salt treatment, but then its concentration and redox state progressively decreased. Concomitantly, the antioxidant enzymes involved in ascorbate and glutathione regeneration were modified under salt stress treatments. In conclusion, the increase in ascorbate levels and the maintenance of the redox state seem to be critical for root growth and development under salt stress.

The systems are required to understand and present at higher levels of abstractions to perform ch... more The systems are required to understand and present at higher levels of abstractions to perform changes or re-engineer to meet the current requirements. The software systems drift away from the existing implemented source code and the documentations due to the changes. The high level models are used for the purpose of recovering the artifacts and understanding the system to perform the maintenance activities. This paper presents an approach to develop the high level models from the existing source code and documents.

This paper gives an insight into the working and efficiency of the two basic algorithms used for ... more This paper gives an insight into the working and efficiency of the two basic algorithms used for parameter estimation: Ordinary Least Squares (OLS) and Recursive Least Squares (RLS). A simple DC motor is taken here as an example of a SISO system. The input voltage and the output in the form of rotations of the motor are given to the parameter estimator. The parameters of the motor are determined using both the algorithms and, hence, a comparison is given on the basis of those results.

Amino Acids, 2009

Post-translational modifications such as glycosylation are important for changing the properties ... more Post-translational modifications such as glycosylation are important for changing the properties and functions of proteins. To analyze the importance of glycosylation during cold stress in rice, a proteomics approach was used. Proteins extracted from the basal part of rice leaf sheaths were separated by two-dimensional polyacrylamide gel electrophoresis, and subjected to lectin blot analysis using concanavalin A. From a total of 250 detected proteins, 22 reacted with the lectin, suggesting that they were N-glycosylated proteins. To determine how N-glycosylation of these proteins is affected by cold stress, rice seedlings were incubated at 5°C for 48 h, and proteins extracted from the basal parts of leaf sheaths were analyzed by the lectin blot assay. Cold stress changed the reactivity toward the lectin for 12 of the 22 glycoproteins. The identity of the 12 proteins was determined by protein sequencing and mass spectrometry with the majority of these glycoproteins being categorized as involved in energy production. Furthermore, calreticulin, one of the 12 glycoproteins, was also phosphorylated as a result of cold stress. These results indicate that cold stress of the basal parts of rice leaf sheaths changes the glycosylation and phosphorylation profiles of calreticulin, a key protein that regulates the quality control of other proteins.

The systems are required to understand and present at higher levels of abstractions to perform th... more The systems are required to understand and present at higher levels of abstractions to perform the changes and meet the current requirements. When the changes are performed, the source code drifts away from the existing available system documentation (specifications, design, manuals), which represent the functionality of the software systems. The software systems are developed using the multi-languages with different dialects and scripts. This paper presents a clustering approach using the available source code, documentation, experience and knowledge about the domain and application to cluster the source code. The source code clustering is used for the purpose of recovering the artifacts, understanding the system and identifying the relationships among the source code to plan, design and execute the changes in the software systems.

The idea of the absurd is a common theme in many existentialist works. The philosophy that encomp... more The idea of the absurd is a common theme in many existentialist works. The philosophy that encompasses the absurd is referred to as absurdism. While absurdism may be considered a branch of existentialism, it is a specific idea that is not necessary to an existentialist view Absurdism is the conflict of human existence,with the human tendency to look for meaning and value in life and human inability to find any, and will ultimately fail. Existentialism is how human address this conflict, by knowing the lack of objective meaning it is therefore the responsibility of individuals to give their own lives meaning. So absurdism doesn't state that there isn't any meaning, but it is impossible for humans to know it whereas the existentialist explicitly believe there isn't any value at all.