Purification and preliminary characterization of the soybean glyoxysomal aspartate aminotransferase isozyme

The glyoxysomal isozyme of aspartate aminotransferase (EC 2.6.1.1: AAT1) wa s purified from soybean cotyledons. AAT1 was separated from other soybean A AT isozymes by DEAE ion exchange chromatography and then purified to electr ophoretic homogeneity by immunoaffinity chromatography. The purified isozym e contained a single polypeptide as detected on SDS PAGE with an estimated M-r of 42 000 Da. The glyoxysomal AAT had a broad pH optimum from 7.5 to 10 .5 with maximal activity found at 9.5. The apparent K-m values were 4.7 mM for aspartate, 0.11 mM for 2-oxoglutarate, 49 mM for glutamate, and 0.11 mM for oxaloacetate. Kinetic parameters and size of the AAT1 polypeptide sugg est this glyoxysomal form of AAT is similar to AAT isozymes targeted to oth er subcellular compartments in plants. (C) 1998 Elsevier Science Ireland Lt d. All rights reserved.