Characterization of methylmalonyl-CoA mutase involved in the propionate photoassimilation of Euglena gracilis Z

Significant accumulation of the methylmalonyl-CoA mutase apoenzyme was observed in the photosynthetic flagellate Euglena gracilis Z at the end of the logarithmic growth phase. The apoenzyme was converted to a holoenzyme by incubation for 4 h at 4°C with 10 μM 5′-deoxyadenosylcobalamin, and then, the holoenzyme was purified to homogeneity and characterized. The apparent molecular mass of the enzyme was calculated to be 149.0 kDa ± 5.0 kDa using Superdex 200 gel filtration. SDS–polyacrylamide gel electrophoresis of the purified enzyme yielded a single protein band with an apparent molecular mass of 75.0 kDa ± 3.0 kDa, indicating that the Euglena enzyme is composed of two identical subunits. The purified enzyme contained one mole of prosthetic 5′-deoxyadenosylcobalamin per mole of the enzyme subunit. Moreover, we cloned the full-length cDNA of the Euglena enzyme. The cDNA clone contained an open reading frame encoding a protein of 717 amino acids with a calculated molecular mass of 78.3 kDa, preceded by a putative mitochondrial targeting signal consisting of nine amino acid residues. Furthermore, we studied some properties and physiological function of the Euglena enzyme.