Selective binding of divalent cations toward heme proteins  

作　　者：Pijush Basak Tanay Debnath Rajat Banerjee Maitree Bhattacharyya 

机构地区：[1]Department oJBiochemistry, University of Calcutta, 35, Ballygunge Circular Road, Kolkata-700019, India [2]Department of Chemistry, Indian Institute of Chemistry Kanpur, Kanpur 208016, U. P. India [3]Department of Biotechnology, University of Calcutta,35, Ballygunge Circular Road, Kolkata-700019, India

出　　处：《Frontiers in Biology》2016年第1期32-42,共11页生物学前沿（英文版）

摘　　要：Potential toxicity of transition metals like Hg, Cu and Cd are well known and their affinity toward proteins is of great concern. This work explores the selective nature of interactions of Cu2＋, Hg2＋ and Cd2＋ with the heme proteins leghemoglobin, myoglobin and cytochrome C. The binding profiles were analyzed using absorbance spectrum and steady-state fluorescence spectroscopy. Thermodynamic parameters like enthalpy, entropy and free energy changes were derived by isothermal calorimetry and consequent binding parameters were compared for these heme proteins. Free energy （AG） values revealed Cu2＋ binding toward myoglobin and leghemoglobin to be specific and facile in contrast to weak binding for Hg2＋ or Cd2＋ . Time correlated single photon counting indicated significant alteration in excited state lifetimes for metal complexed myoglobin and leghemoglobin suggesting bimolecular collisions to be involved. Interestingly, none of these cations showed significant affinity for cytochrome c pointing that, presence of conserved sequences or heme group is not the only criteria for cation binding toward heme proteins, but the microenvironment of the residues or a specific folding pattern may be responsible for these differential conjugation profile. Binding of these cations may modulate the conformation and functions of these biologically important proteins.Potential toxicity of transition metals like Hg, Cu and Cd are well known and their affinity toward proteins is of great concern. This work explores the selective nature of interactions of Cu2＋, Hg2＋ and Cd2＋ with the heme proteins leghemoglobin, myoglobin and cytochrome C. The binding profiles were analyzed using absorbance spectrum and steady-state fluorescence spectroscopy. Thermodynamic parameters like enthalpy, entropy and free energy changes were derived by isothermal calorimetry and consequent binding parameters were compared for these heme proteins. Free energy （AG） values revealed Cu2＋ binding toward myoglobin and leghemoglobin to be specific and facile in contrast to weak binding for Hg2＋ or Cd2＋ . Time correlated single photon counting indicated significant alteration in excited state lifetimes for metal complexed myoglobin and leghemoglobin suggesting bimolecular collisions to be involved. Interestingly, none of these cations showed significant affinity for cytochrome c pointing that, presence of conserved sequences or heme group is not the only criteria for cation binding toward heme proteins, but the microenvironment of the residues or a specific folding pattern may be responsible for these differential conjugation profile. Binding of these cations may modulate the conformation and functions of these biologically important proteins.

关 键 词：heme proteins divalent cations fluorescence quenching isothermal calorimetry time correlated single photoncounting （TCSPC） 

分 类 号：O614.121[理学—无机化学] TQ463[理学—化学]