Enantiopure epoxides are of great interest in industry as they are valuable intermediates in organic synthesis for the production of fine chemicals, perfumes, polymers or pharmaceuticals. Numerous enzymes have been identified for their ability to catalyze the production of enantiomerically pure epoxides. This includes styrene monooxygenases, cytochrome P450 monooxygenases or unspecific peroxygenases. Recently, investigations on a glutathione S-transferase (GST) from the glutathione-dependent styrene degradation pathway revealed its ability to be used for the production of enantiopure aromatic epoxides.

Interestingly, there are no known GSTs that demonstrate the ability to perform the enantioselective conversion of aliphatic epoxides. As a consequence, an actinobacterial GST capable of converting aliphatic epoxides enantioselectively was screened for. One promising GST, designated RhoIsoI, was found in the isoprene-degrading actinobacterium Rhodococcus opacus PD630 and was subsequently biochemically characterized.

In this study, the GST was initially analyzed for their ability to convert aliphatic epoxides with an enantiomeric preference via GC-FID. The results demonstrated that RhoIsoI exhibited significantly higher activity towards the aliphatic epoxide isoprene monoxide in contrast to the aromatic styrene oxide. An enantiomeric preference for both substrates was observed. Size exclusion chromatography revealed that this enzyme occurs as a homodimer. Spectrophotometric measurements using the model substrate CDNB showed optimal thermal stability at 25°C for this enzyme. Different additives had no significant positive or negative influence on the activity of RhoIsoI except for zinc and nickel sulphate. In this case, the relative activity decreased to 24% and 27%, respectively.

Overall, this study presents a promising GST capable of converting the aliphatic isoprene monoxide with high activity. However, detailed investigation on more aliphatic epoxides shall demonstrate the potential of using RhoIsoI to produce enantiopure epoxides.