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Journal of Histochemistry and Cytochemistry, Vol. 45, 685-694, Copyright © 1997 by The Histochemical Society, Inc.
Cellular Distribution of Branched-chain Amino Acid Aminotransferase Isoenzymes Among Rat Brain Glial Cells in Culture
M. Gabriele Bixela,
Susan M. Hutsonb, and
Bernd Hamprechta
a Physiologisch-chemisches Institut der Universität, Tübingen, Germany
b Department of Biochemistry, Bowman Gray School of Medicine, Winston-Salem, North Carolina
Correspondence to:
Bernd Hamprecht, Physiologisch-chemisches Institut der Universität, Hoppe-Seyler-Str. 4, D-72076 Tübingen, Germany.
The first step in the catabolism of branched-chain amino acids (BCAA), reversible transamination, is catalyzed by one of the two isoforms of branched-chain amino acid aminotransferase (BCAT). The mitochondrial isoenzyme (BCATm) is widely distributed among tissues, whereas the cytosolic isoenzyme (BCATc) is restricted to only a few organs. Remarkably, BCATc is the prominent isoenzyme found in brain. The physiological significance of the subcellular compartmentation of BCAT is still not understood. To contribute to the elucidation of the cellular distribution of the two isoenzymes in brain, we used cultured rat glial cells in an immunocytochemical study to determine the pattern of BCAT isoenzyme expression by glial cells. Antiserum against BCATm generated a punctate staining pattern of astroglial cells, confirming the mitochondrial location of this isoenzyme. In contrast, the cytosol of galactocerebroside-expressing oligodendroglial cells and O2A progenitor cells displayed intense staining only for BCATc. In addition, subpopulations of astroglial cells exhibited BCATc immunoreactivity. The presence of BCATm in astrocytes is consistent with the known ability of these cells to oxidize BCAA. Furthermore, our results on BCATc provide support for the hypothesis that BCATs are also involved in nitrogen transfer from astrocytes to neurons. (J Histochem Cytochem 45:685-694, 1997)
Key Words:
astroglial cells, energy metabolism, immunocytochemistry, nitrogen metabolism, oligodendroglial cells, O2A progenitor cells

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