Abstract: The interaction between myohemoglobin (Mb) and prodigiosin (PG) was investigated by UV-visible, fluorescence, synchronous fluorescence, FT-IR and circular dichroism (CD) spectroscopic techniques. The UV absorption of Mb was increased in the presence of PG, indicating that PG interacted mainly with amino acid residues on the outside of Mb. The peak fluorescence intensity of Mb was increased through its interaction with PG. Moreover, the binding constant between them was decreased with increasing temperature. The enthalpy change (ΔH) was －25.293 kJ/mol, and the entropy change (ΔS) was －10.238 J/(mol•s) at 298 K and －10.239 J/(mol•s) at 310 K as calculated according to the thermodynamic equation. The data showed that Van der Waals force played a critical role in the interaction between Mb and PG. Synchronous fluorescence spectroscopic analysis revealed alteration of the microenvironment of amino acid residues as a result of the interaction between both materials. FT-IR analysis showed alternation of the secondary structure of Mb induced by the interaction of amide groups in its polypeptide chains with PG. CD analysis demonstrated a reduction in α-helix content of Mb due to PG-induced alteration of the secondary structure. 

Key words: prodigiosin, myohemoglobin, UV-visible absorption, fluorescence spectrum, FT-IR, circular dichroism