Authors: Pannuru Venkatesu
Protein stability in ionic solution depends on the delicate balance between protein-ion and ion-ion interactions. To address the ion specific effects on the enzyme in detail, we have examined the stability of myoglobin (Mb) in the presence of nine ammonium based ionic liquids (ILs), such as diethylammonium acetate (DEAA), diethylammonium hydrogen sulfate (DEAS), diethylammonium dihydrogen phosphate (DEAP), triethylammonium acetate (TEAA), triethylammonium hydrogen sulfate (TEAS), triethylammonium dihydrogen phosphate (TEAP), trimethylammonium acetate (TMAA), trimethylammonium hydrogen sulfate (TMAS) and trimethylammonium dihydrogen phosphate (TMAP). Later, fluorescence and circular dichroism (CD) spectroscopy experiments are also used to study the influence of ammonium ILs on structure and stability of Mb. Our experimental results reveal that more viscous ILs (sulphate or phosphate ions) are stabilizers and therefore more biocompatible for Mb structure. Surprisingly, the less viscous ILs such as acetate anion based ILs are destabilizers for the native structure of Mb. Our results explicitly elucidate that anion variation has significantly influenced on Mb stability efficiency more than cation variation. This study provides insight into anion effects on protein stability and serves as an example of how these intrasolvent interactions can be leveraged to enhance the stability.