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Title: PURIFICATION AND PRELIMINARY CHARACTERIZATION OF THE SOYBEAN GLYOXYSOMAL ASPARTATE AMINOTRANSFERASE ISOZYME

Author
item STEPHENS, AMY - BUFFALO STATE COLLEGE
item GEBHARDT, JOAN - MISC.
item Matthews, Benjamin
item WADSWORTH, GREGORY - BUFFALO STATE COLLEGE

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Aspartate aminotransferase (AAT) is central to carbon and nitrogen metabolism of cells. In plants it is involved in ammonia assimilation, recycling carbon skeletons and synthesizing aspartate. There are several forms of AAT found in plants. One form AAT1 is located in a small organelle called the glyoxysome. We purified AAT1 to study its characteristics for comparison with those of other cellular forms of AAT. The kinetic properties of glyoxysomal AAT1 are quite similar to those of other cellular forms of AAT with only minor differences being noted. The glyoxysomal and cytosolic forms of AAT are of similar size and of nearly identical primary structure, supporting other evidence that they are both encoded by the same gene. This information is important to scientists interested in genetically engineering AAT genes to alter the flow of carbon and nitrogen in plants.

Technical Abstract: Aspartate aminotransferase (AAT) is central to carbon and nitrogen metabolism of cells. In plants it is involved in ammonia assimilation, recycling carbon skeletons, shuttling carbon and synthesizing aspartate. The glyoxysomal isozyme of aspartate aminotransferase (AAT1) was purified from soybean cotyledons. AAT1 was separated from other soybean AAT isozymes sby ion exchange chromatography and then purified to electrophoretic homogeneity by immunoaffinity chromatography. The purified isozyme contained a single polypeptide as detected on SDS PAGE with and estimated molecular mass 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 Km 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 suggest this glyoxysomal form of AAT is similar to AT isozymes targeted to other subcellular compartments in plants. This information is important to scientists working on nitrogen distribution in plants.