Controversial effect of two methylguanidine-based ionic liquids on firefly luciferase.

The importance and applicability of ionic liquids (ILs) in biocatalysis have been well recognized. ILs have growing interest as new and highly efficient reaction mediums for biocatalytic reactions, but as a reaction milieu for firefly luciferase has not been tested. In this report, the effects of two tetramethylguanidine-based ionic liquids on the activity and stability of Photinus pyralis luciferase were investigated. In spite of a common cationic part, luciferase activity increased up to 0.25 M of [TMG][Lac] but decreased in the presence of similar concentrations of [TMG][Pro]. Optimum temperature and thermal stability studies show more stability of luciferase only in the presence of [TMG][Lac]. The change in light intensity of firefly luciferase in the presence of both ILs was brought about without effect on bioluminescence emission spectra. The rate of light decay in the presence of both ILs was slower than native luciferase.