Purification and Characterization of an Anaerobically Induced Alanine Aminotransferase from Barley Roots

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Abstract
Alanine aminotransferase (AlaAT, EC 2.6.1.2) is an enzyme that is induced under anaerobic conditions in cereal roots. In barley (Hordeum vulgare L.) roots, there are a number of isoforms of AlaAT. We have identified the anaerobically induced isoform and have purified it to homogeneity. The isolation procedure involved a two-step ammonium sulfate precipitation, gel filtration, ion-exchange chromatography, and chromatofocusing. The enzyme was purified approximately 350-fold to a specific activity of 2231 units/milligram protein. The apparent molecular masses of the native and sodium dodecyl sulfate-denatured AlaAT proteins are 97 and 50 kilodaltons, respectively, indicating that the native enzyme is probably a homodimer. AlaAT has a number of interesting characteristics when compared with other plant aminotransferases. AlaAT does not require the presence of pyridoxyl-5-phosphate to retain its activity, and it appears to be very specific in the reactions that it will catalyze.