Purification and some properties of alanine aminotransferase from Candida maltosa

Alanine aminotransferase (AlaAT; EC 2.6.1.2) was purified to homogeneity from Candida maltosa that was grown on L-alanine as the sole source of carbon and nitrogen. The enzyme has a molecular mass of 99kDa and consists of two subunits of equal molecular mass (52 kDa). Each subunit binds one mole of PLP. The enzyme has an isoelectric point of 5.3 and an optimum pH of 6.0-7.5. The spectroscopic profile and an inhibition experiment showed that both PLP and free-SH groups are directly involved in the enzymatic catalysis. In the N-terminal region of the enzyme, the consensus sequence (five amino acids) that commonly appears in mammalian and higher plant enzymes is present. Compared with mammalian enzyme, the Candida AlaAT is heat-sensitive and a little looser in substrate specificity, and its affinity towards L-alanine is high.