Purification and characterization of serine–glyoxylate aminotransferase from a serine‐producing methylotroph, Hyphomicrobium methylovorum GM2

Serine–glyoxylate aminotransferase was purified to complete homogeneity from a serine‐producing methylotrophic bacterium, Hyphomicrobium methylovorum GM2, which possesses the serine pathway. This is the first microbial serine–glyoxylate aminotransferase to be purified. The enzyme has a molecular mass of about 140 kDa and consists of four subunits of identical mass, i.e. 40 kDa. The holoenzyme exhibited absorption maxima at 282 nm and 408 nm, and a shoulder at about 315–345 nm in potassium phosphate pH 7.0; it contained 4 mol pyridoxal 5′‐phosphate/mol enzyme. Isoelectric focusing showed that the enzyme had a pI value of 6.9. The K m values for glyoxylate and L‐serine were 0.23 mM and 4.98 mM, respectively, and the enzyme showed high specificity for these substrates. The transamination between glyoxylate and L‐serine seemed to be nearly irreversible. These data indicated that this serine–glyoxylate aminotransferase plays an essential role in methanol assimilation through the serine pathway in H. methylovorum GM2.