Studies on heme release from normal and metal ion reconstituted hemoglobin mediated through ionic surfactant

Abstract

The interaction of metal-substituted hemoglobin (MHb), where M = Ni and Cu (T-state with no O₂ and CO binding capability) and Fe (R-state when CO is bound), with cationic cityl trimethyl ammonium bromide (CTAB) and anionic (sodium dodecyl sulfate—SDS) surfactants has been studied using spectroscopic techniques—UV-visible, electron paramagnetic resonance (EPR), and Fourier transform–Raman—with additional supportive evidence coming from conductivity measurements. We observed the loss of 5-coordination in all three hemoglobins below the critical micelle concentration (CMC) of surfactant, with noticeable differences, suggesting differing mechanisms involved in this process. In addition, above the CMC, Ni- and Cu-hemes were found to leave their proteins more easily than Fe-heme, presumably due to weaker or no bond with the proximal histidine in the former. The released heme is stabilized by micellar media through a hydrophobic interaction process. Of the two surfactants, CTAB seems to be capable of releasing the heme better than SDS and it is attributed to the greater hydrophobicity of CTAB though the charge of the surfactant plays an important role.