[L-alanine: 2-ketoglutarate aminotransferase from maize embryo with complex kinetic properties for l-alanine (author's transl)].

The activity of L-Alanine: 2-oxoglutarate aminotransferase (E.C. 2.6.1.2) has been studied in maize (Zea mays) embryo. Crude extracts were fractioned with ammoniun sulfate to obtain low activity preparations of other aminotransferases present in crude extracts. The enzyme shows normal hyperbolic saturation curves for the substrasts: Pyruvate (Km 1 mM), 2-oxoglutarate (Km 0.4 mM) and L-Glutamate (Km 0.07 mM). However, it shows complex kinetics properties for the substrate L-Alanine, giving sigmoid saturation curves for L-Alanine at low but not at high fixed 2-oxoglutarate concentrations. These last results point to a regulation of the of L-Alanine degradation, which takes place during the germination of maize. Together with L-Glutamate and L-Alanine, the enzyme only seems to use L-Serine and L-Cysteine and their cetoacids.