Purification of a Protein Exhibiting Isoleucine 2-epimerase Activity from Lactobacillus otakiensis JCM 15040

Abstract

Prominent accumulation of D-leucine, D-allo-isoleucine and D-valine was observed in the culture medium of the heterofermentative bacterial species, Lactobacillus otakiensis (L. otakiensis) JCM 15040. The racemase enzyme that resulted in this accumulation, isoleucine 2-epimerase, was purified from the bacterial cells. This is the first reported observation of such production of D-branched chain amino acids in lactic acid bacteria, and the first example of a racemase with isoleucine 2-epimerase activity in any organisms. In the described protocol, we introduce methods for purification of this protein from L. otakiensis JCM 15040. Because no specific ligand that has high affinity for this enzyme has been identified, the purification was performed using ammonium sulfate fraction, four types of column chromatography and preparative Native-PAGE, not using an affinity column chromatography. We hope that the protocol will provide useful information for purification of an enzyme that cannot easily be purified using an affinity column chromatography.