Purification and properties of betaine aldehyde dehydrogenase from Avena sativa

Betaine aldehyde dehydrogenase (BADH; EC 1.2.1.8) is the enzyme that catalyzes the second step in the synthesis of the osmoprotectant, glycine betaine. NAD-dependent BADH was purified from Avena sativa shoots by DEAF Sephacel, hydroxyapatite, 5'-AMP Sepharose 413, Mono Q and TSK-GEL column chromatographies to homogeneity by the criterion of native PAGE, and the properties of BADH were compared with those of aminoalde-hyde dehydrogenase purified to homogeneity from A. sativa. The molecular mass estimated by both gel filtration using TSK-GEL column and Sephacryl S-200 was 120 and 115 kDa, respectively. The enzyme is a homodimer with a subunit molecular mass of 61 kDa as shown by SDS-PAGE. The pI value of the enzyme was found to be 6.3. The purified enzyme catalyzed not only the oxidation of betaine aldehyde (BAL), but also that of aminoaldehydes, 3-aminopropionaldehyde (APAL), 4-aminobutyraldehyde (ABAL), and 4-guanidinobutyraldehyde (GBAL). The K-m values for BAL, APAL, ABAL and GBAL were 5 x 10(-6), 5.4 x 10(-7), 2.4 x 10(-5) and 5 x 10(-5) M, respectively. APAL showed substrate inhibition at a concentration of 0.1 mM. A fragment of BADH cleaved by V8 protease shared homology with other plant BADHs.