Importance of C3=C4 double bondof plant alkaloid Harmine on its binding interaction with Hemoglobin: Multi-spectroscopic and molecular modelling studies

Harmine and harmaline are two structurally similar β-carboline plant alkaloids with various therapeutic properties, having difference in C3 = C4 double bond only. Nature of the interaction between hemoglobin (Hb) and harmine and harmaline was investigated in this study by employing different spectroscopic methods and molecular modeling. The spectrum of Hb showed hypochromic changes in the presence of both harmine and harmaline but with different efficiencies. The fluorescence quenching of harmine and harmaline occurred in the presence of Hb indicating stronger interation of harmine with Hb. Stoichiometry study revealed that both harmine and harmaline interact with Hb in around 1:1 ratio. The circular dichroism study demonstrate no conformational change of Hb in the presence of alkaloids. From the melting study, it was found that both harmine and harmaline do not affect the stability of Hb. Molecular modeling study supported the above findings that harmine containing the C3 = C4 double bond in its structure, interacts strongly with Hb on the surface of α2 chain compared to harmaline. This study helps us to understand that slight structural differences in harmine and harmaline can alter interaction properties significantly and these key informations may help in the drug discovery processes.