PURIFICATION AND CHARACTERIZATION OF OLIGOMERIC SPECIES OF AN AROMATIC AMINO ACID AMINOTRANSFERASE FROM LACTOCOCCUS LACTIS SUBSP. LACTIS S3 (original) (raw)

1998, Journal of Food Biochemistry

Two oligomeric species of an aromatic amino acid aminotransferase (Ar-AT) were purified and characterized from Lactococcus lactis subsp. lactis S3. The more abundant species, Ar-AT1, was purified over 2,200-fold with a 3% recovery. The molecular masses of Ar-AT1 were determined to be 42 kDa and 84 kDa by SDS-PAGE and gel filtration, respectively. The molecular masses of the less abundant species, Ar-AT2, were 42 kDa and 170 kDa, respectively. Both Ar-AT1 and Ar-AT2 have identical N-terminal sequences which indicates they are homodimeric and homotetrameric forms of the same enzyme. The Ar-ATs catalyze pyridoxal-5′-phosphate dependent transamination of Phe, Tyr, Trp, Leu and Met utilizing α-ketoglutarate as the amino acceptor. Km values of the two Ar-ATs for Trp, Tyr and Phe ranged from 0.65 to 2.43 mM. However, differences were observed in the pI and specific activities between the two Ar-ATs. The pI values of Ar-AT1 and Ar-AT2 were 4.63 and 3.93, respectively. The Vmax/Km ratios of Ar-AT2 for Trp, Tyr and Phe were three-fold greater than that of Ar-AT1, indicating that Ar-AT2 is more catalytically efficient on these amino acids than Ar-AT1.