Purification and Characterization of a Rat Brain Aldehyde Dehydrogenase Able to Metabolize gamma-Amino Butyraldehyde to gamma-Aminobutyric Acid

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An enzyme which catalyses dehydrogenation of gamma-aminobutyraldehyde (ABAL) to gamma-aminobutyric acid (GABA) was purified to homogeneity from rat brain tissues by using DEAE cellulose and affinity chromatography on 5'-AMP-Sepharose and Blue agarose, followed by gel filtration. Such an enzyme was first purified from mammalian brain tissues, and was identified as isoenzyme of aldehyde dehydrogenase. It has an 210 kDa determined by PAEG, and appeared to be composed of subunits of 50 kDa. Substrate specificity of the enzyme toward ABAL was higher than those of aldehyde dehydrogenases from human liver (E2), and was lower than those of ABAL dehydrogenase from human liver (E3). The molecular weight and relative amino acid composition of the enzyme are also similar to those of E1 and E2. Polyclonal and monoclonal antibodies against the purified enzyme were generated. Both antibodies reacted weakly but significantly with a molecule of 50 kDa band of the enzyme by SDS-PAGE, western blot analysis. By immunohistochemical analysis of the rat brains, antibodies showed positive, homogenous staining in the cytoplasms of the nerve cells without any special localization or tissue distribution of the reactive products. The existence of this enzyme in mammalian brain seems to be related to a glutamate decarboxylase-independent pathway for GABA synthesis from putrescine.