• S Ramasamy

      Articles written in Journal of Chemical Sciences

    • Surfactant-induced stabilization of four-coordinated hemes in reconstituted hemoglobins

      B Venkatesh S Ramasamy V Swarnalatha J Santhanalakshmi R Asokan J M Rifkind P T Manoharan

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      A transition from 5-coordination to 4-coordination metal centres of porphyrins in carbonmonoxy Fe(II), Cu(II) and Ni(II) hemoglobins is observed as a consequence of ionic surfactant interactions with metalloproteins through UV-Vis studies. SDS (anionic) and CTAB (cationic) surfactants are used. Values of heme partition coefficient (K) between globin and surfactant show that, in both CTAB and SDS, partitioning increases proportionately with surfactant concentration for a fixed concentration of hemoglobin. The interactions seem to be mainly hydrophobic in nature with metalloproteins, though coordination and coulombic interactions may also play a minor role in CTAB and SDS respectively. The present study provides new insight into reconstituted hemoglobin-surfactant interaction.

    • Metal ion coordination in ‘R’ and ‘T’ state hybrid hemoglobins as revealed by optical, EPR and sulphhydryl reactivity studies

      S Ramasamy Swarnalatha Venkateshrao J M Rifkind P T Manoharan

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      The sulphhydryl environment in various mixed-metal hybrid hemoglobins, viz. α2(Cu)-β2(FeCO), α2(FeCO)-β2(Cu), α2(Cu)-β2(Ni), α2(Ni)-β2(Cu), was studied by reacting them with the sulphhydryl reagent, 4,4′-dithiodipyridine (4-PDS). The reactivity was compared with that of HbCO, NiHb and CuHb. It is found that there exists a correlation between conformational change and metal ion environment, not only at the extreme R and T states but also the intermediate conformations. EPR examinations of these hybrids show that both in R state-[Cu(II)-Fe(II)] and T state-[Cu(II)-Ni(II)] hybrids at neutral pH and in the absence of IHP, CuPPIX, irrespective of the subunit in which it is present, has a mixed-metal ion environment: Species 1, a five-coordinated Cu2+ complex with strong proximal histidine bond and species 2, a four-coordinated complex without any covalent linkage with Nε F8-histidine.

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