Physicochemical and conformational studies on interaction of myoglobin with an amino-acid based anionic surfactant, sodium N-dodecanoyl sarcosinate (SDDS)

Abstract

Physicochemical and conformational studies on the interaction between horse myoglobin, a monomeric water soluble heme protein and sodium N-dodecanoyl sarcosinate (SDDS), an amino-acid based anionic surfactant have been performed at different pHs using surface tension, viscosity, UV–vis and fluorescence spectroscopy, circular dichroism, isothermal titration calorimetry and differential scanning calorimetry. Myoglobin shows surface activity, according to the surface tension measurement. Protein forms aggregates with surfactant molecules and becomes unfolded with increasing SDDS concentration. Again, when concentration of myoglobin increases, the binding ratio decreases; whereas heme changes its spin and coordination number with increasing surfactant concentration. α-Helicity of myoglobin decreases with increase in concentration of surfactant, while β-sheet and random coil appear. The temperature of transition of myoglobin and the enthalpy of thermal denaturation also change at higher concentration of SDDS. The myoglobin-SDDS interaction at different pH, ranging from 5 to 8 has been studied and it shows that pH has very little effect on the conformational change of the myoglobin-SDDS system.