Purification and properties of alanine aminotransferase from maize (Zea mays L.) leaves

Alanine aminotransferase (ALaAT, EC 2.6.1.2) from leaves of 14-day-old maiz e seedlings was purified over 1600-fold to electrophoretical homogeneity. S pecific activity of the purified enzyme measured with L-alanine and 2-oxogl utarate as substrates was 2125 nkat.(mg protein)(-1) at 30 degrees C. The m olecular weights of the native and sodium dodecyl sulfate - denatured AlaAT protein were 95 kDa and 50 kDa respectively, indicating that the native en zyme rs probably a homodimer. AlaAT almost exclusively catalyzed amino grou p transfer from L-alanine to 2-oxoglutarate and the reverse reaction. The i nhibitory experiments showed that pirydoxal phosphate is directly involved in the enzymatic catalysis and the enzyme molecule contains essential SH gr oups. The use of phenylglyoxal demonstrated the presence of arginine residu e as anionic binding site in the active centre of AlaAT.