@article { ISI:000245519000047, title = {Active site directed chemical modification of alpha-galactosidase from bacillus stearothermophilus (NCIM 5146): involvement of lysine, tryptophan and carboxylate residues in catalytic site}, journal = {Enzyme and Microbial Technology}, volume = {40}, number = {5}, year = {2007}, month = {APR}, pages = {1312-1320}, publisher = {ELSEVIER SCIENCE INC}, type = {Article}, address = {360 PARK AVE SOUTH, NEW YORK, NY 10010-1710 USA}, abstract = {

The catalytic amino acid residues of the extracellular a-galactosidase (alpha-D-galactoside galactohydrolase; EC 3.2.1.22) from Bacillus stearothermophilus NCIM 5146 were investigated by pH dependence and chemical modification studies. These results suggested that carboxylate and a lysine residue take part in catalysis and only lysine residues were essential for substrate binding. Carbodiimide mediated chemical modification of the enzyme also supported that a carboxylate residue located in the active site act as a nucleophile base in substrate cleavage. Acylation and reductive methylation of lysine residues by acetic, citraconic anhydride and sodium borohydride suggested that four protonated lysine residues carrying positive charge on its epsilon-amino group provides the positive charge density for binding of the substrate. Additionally four tryptophan residues also found near to the active site and in a moderately hydrophobic environment. Kinetic and thermal inactivation study of modified enzyme indicated that these tryptophan residues might have a role in the catalytic site as well as in the thermal stabilization of active site conformation at higher temperature. (c) 2006 Elsevier Inc. All rights reserved.

}, keywords = {Active site, alpha-galactosidase, Bacillus stearothermophilus, carboxylate, Chemical modification, lysine, Tryptophan}, issn = {0141-0229}, doi = {10.1016/j.enzmictec.2006.10.004}, author = {Gote, M. M. and Khan, Mohammad Islam and Khire, Jayant Malhar} } @article { ISI:000272134300006, title = {Interaction of alpha-mannosidase from aspergillus fischeri with glycosidase inhibitors, metal ions and group specific reagents}, journal = {Research Journal of Biotechnology}, volume = {4}, number = {4}, year = {2009}, month = {NOV}, pages = {39-48}, publisher = {RESEARCH JOURNAL BIOTECHNOLOGY}, address = {SECTOR A-80, SCHEME NO 54, VIJAY NAGAR, A B ROAD, INDORE, 452 010 MP, INDIA}, abstract = {

As an initial step towards using alpha-mannosidase as a target against anticancer drugs, inhibition studies of a model enzyme, class II alpha-mannosidase from Aspergillus fischeri in presence of polyhydroxy piperidine derived glycosidase inhibitors, metal ions and amino acid specific reagents were carried out to reveal the sensitivity of the enzyme. Three of the derivatives (Compound 20, 32 and 39)(11) showed competitive inhibition (K(i) =45, 48 and 235 mu M) and the binding of the inhibitors to the enzyme was entropically driven. Among the metal ions checked, Cu(++) (K(i) = 21nm) and Se(++) ions (K(i) = 32 mu M) showed noncompetitive and Co(++) (K(i) = 1.195 mM) showed competitive inhibition of the enzyme activity with insignificant change in the secondary structure of the protein. The above studies exhibit the Potential of the enzyme in studying anticancer drugs. Treatment of the enzyme with group specific reagents showed the presence of carboxylate, Arg and Cys at the active site. Substrate protection studies and kinetics of the modified enzyme confirmed the above results. Trp and His at the active site were observed to be in proximity.

}, keywords = {active-site, alpha-Mannosidase, Chemical modification, Glycosidase inhibitors, metal ions}, issn = {0973-6263}, author = {Shashidhara, K. S. and Gaikwad, S. M. and Khan, Mohammad Islam and Bharadwaj, Kishor Chandra and Pandey, G.} } @article { ISI:000265921000002, title = {Purification and characterization of putative alkaline [Ni-Fe] hydrogenase from unicellular marine green alga, tetraselmis kochinensis NCIM 1605}, journal = {Microbiological Research}, volume = {164}, number = {2}, year = {2009}, month = {FEB}, pages = {131-137}, publisher = {ELSEVIER GMBH, URBAN \& FISCHER VERLAG}, address = {OFFICE JENA, P O BOX 100537, 07705 JENA, GERMANY}, abstract = {

Hydrogenase enzyme from the unicellular marine green alga Tetraselmis kochinensis NCIM 1605 was purified 467 fold to homogeneity. The molecular weight was estimated to be similar to 89kDa by SDS-PAGE. This enzyme consists of two subunits with molecular masses of similar to 70 and similar to 19 kDa. The hydrogenase was found to contain 10 g atoms of Fe and 1 g of atom of Ni per mote of protein. The specific activity of hydrogen evolution was 50 mu mol H-2/mg/h of enzyme using reduced methyl viologen as an electron donor. This hydrogenase enzyme has pl value similar to 9.6 representing its alkaline nature. The absorption spectrum of the hydrogenase enzyme showed an absorption peak at 425 nm indicating that the enzyme had iron-sulfur clusters. The total of 16 cysteine residues were found per mote of enzyme under the denaturing condition and 20 cysteine residues in reduced denatured enzyme indicating that it has two disulfide bridges. (C) 2007 Published by Elsevier GmbH.

}, keywords = {Characterization, Chemical modification, Ni-Fe hydrogenase, Tetraselmis kochinensis, Unicellular green algae}, issn = {0944-5013}, doi = {10.1016/j.micres.2006.11.006}, author = {Bhosale, Siddharth H. and Pant, A. and Khan, Mohammad Islam} } @article { ISI:000274401600036, title = {Steady state and time resolved fluorescence quenching and chemical modification studies of a lectin from endophytic fungus fusarium solani}, journal = {Journal of Fluorescence}, volume = {20}, number = {1}, year = {2010}, month = {JAN}, pages = {305-313}, publisher = {SPRINGER/PLENUM PUBLISHERS}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

The solute quenching studies of a lectin from endophytic fungus Fusarium solani were carried out using different quenchers such as acrylamide, succinimide, potassium iodide and cesium chloride. The lectin showed emission maximum at 348 nm indicating relative exposure of tryptophan. The quenchable fraction of the fluorophore was 100\% with acrylamide, whereas it was only 50\% with succinimide. The ionic quenchers iodide and cesium showed opposite effects at different pH. In the case of cesium, raising the pH resulted in increased quenching and accessibility of typtophan residue, while the iodide showed just opposite effect. These studies showed that the single tryptophan residue of the lectin (per monomer) is relatively exposed, and might be in the vicinity of positively charged amino acid residues. Various amino acids of the F. solani lectin were modified using different reagents to obtain information about the hemagglutinating site. The chemical modification studies suggested tyrosine residues can be modified using N-acetylimidazole, which results in complete loss of hemagglutination activity of the lectin. Kinetics of chemical modification suggested involvement of only 2 tyrosine residues. Modification of arginine, cysteine, histidine, lysine, aspartate, glutamate and tryptophan did not result in loss of hemagglutinating activity of the lectin.

}, keywords = {Chemical modification, fluorescence, Fusarium, Lectin, Quenching, Time-resolved}, issn = {1053-0509}, doi = {10.1007/s10895-009-0556-x}, author = {Khan, Feroz and Ahmad, Absar and Khan, Mohammad Islam} }