Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

Biophysical Sciences 2236.1.7.10 Investigation of the interactions of quinone drug like molecules with DNAbasesWe have investigated the mode of interactions of 9,10-anthraquinone (AQ) and 2-methyl-1, 4-naphthoquinone (menadione, MQ) with some DNA bases and their nucleosides in organic homogeneousmedium (acetonitrile/water) and heterogeneous micellar medium using laser flash photolysisand magnetic field effect. In micellar medium MQ supports a dominating H abstraction with adenine(ADN) and adenosine (ADSN) while it leads to a competitive electron transfer (ET) and Habstraction with thymine (THM) and thymidine (THD). On the other hand, AQ preferred ETwith ADN and ADSN while H abstraction seems to be prominent with THM and THD. All suchobservations can be explained by characteristic behavior of the interacting molecules in the confinedenvironment.Adity Bose (neé Chowdhury), Debarati Dey, Chitra Raha, Samita BasuCSD6.1.7.11 Interaction of 4-nitroquinoline 1-oxide with indole derivatives and some relatedbiomolecules: a study with magnetic fieldWe have studied the interaction of 4-nitroquinoline 1-oxide (4NQO) with some indole derivatives,the amino acids, tyrosine and tryptophan and the model proteins, lysozyme and bovine serumalbumin using laser flash photolysis and an external magnetic field. In an aprotic medium, photoinducedelectron transfer (PET) from indoles to 4NQO is accompanied by proton transfer fromthe indole moieties irrespective of the substitution at the N-1 position. For 1,2-dimethylindolehowever, proton abstraction is hindered possibly due to steric effect. In a protic medium, obviouslyproton transfer is possible from the medium and is the dominating reaction following PET. Anotherinteresting observation is that PET takes place preferably from the tryptophan residues rather thanfrom the tyrosine residues.Sharmistha Dutta Choudhury, Chitra Raha, Samita BasuCSD6.1.7.12 Investigation of the mode of interaction of menadione with hen egg whitelysozymeWe have attempted to elucidate the molecular details of the nature of the interaction betweenmenadione (2-methyl-1, 4-naphthoquinone) with hen egg white lysozyme using steady state fluorescencespectroscopy to monitor the binding. A red shifted excited state complex is formed dueto binding of menadione with lysozyme. Laser flash photolysis experiments indicate that this isa charge transfer complex formed by the electron transfer from a tryptophan (Trp) residue of theprotein to the naphthoquinone. Based on circular dichroism data, we have shown that the proteinundergoes significant secondary structural changes with an increase in α-helical content as menadionebinds. Docking studies suggest that menadione lies within hydrogen bonding distance of theindole moiety of Trp 108 of lysozyme.Swagata Banerjee, Sharmistha Dutta Choudhury, Swagata Dasgupta†, Chitra Raha, SamitaBasuCSD