Thermostable ornithine aminotransferase from Bacillus sp. YM-2: purification and characterization

Thermostable L-ornithine: alpha-ketoglutarate delta-aminotransferase (L-ornithine: 2-oxo-acid 5-aminotransferase) [EC 2.6.1.13] was purified to homogeneity from Bacillus sp. YM-2. The enzyme has a molecular weight of about 82,000 and consists of two subunits with identical molecular weights. The enzyme catalyzes transamination from L-ornithine to alpha-ketoglutarate, producing L-glutamate and L-glutamate gamma-semialdehyde, which is spontaneously dehydrated to L-delta 1-pyrroline-5-carboxylate, and the enzyme is most active at 70 degrees C. In addition to L-ornithine, the enzyme unexpectedly acts on D-ornithine, the reaction rate being 6% of that for L-ornithine. The enzyme contains 1 mol each of pyridoxal 5'-phosphate and another vitamin B6 compound per mol. The enzyme released the bound pyridoxal 5'-phosphate, as judged from the absorption at 425 nm on incubation with 2.0 M guanidine hydrochloride. The resultant inactive enzyme still gave a 340-nm peak and contained 1 mol of the vitamin B6 compound. The partial amino acid sequence shows high homology with those of mammalian and yeast ornithine delta-aminotransferases.