Publication: Immunogold localization of mitochondrial aspartate aminotransferase in mitochondria
and on the cell surface in normal rat tissues
Authors
Cechetto, J.D. ; Sadacharan, S.K. ; Berk, P.D. ; Gupta, R.S.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
Mitochondrial aspartate aminotransferase
(mAspAT) (E.C. 2.6.1.1), an important enzyme in amino
acid metabolism, is identical to a fatty acid-binding
protein (FA B Pp m) isolated from plasma membranes of
several cell types. Employing a monospecific polyclonal
antibody to rat mAspAT, we have used immunogold
electron microscopy to study the subcellular distribution
of mAspAT in various mammalian tissues. Immunogold
labeling of rat tissue sections embedded in LR Gold
resin showed strong labeling of mitochondria in all
tissues examined (viz. live r, pancreas, pituitary, spleen,
heart, kidney, submandibular gland). In addition, strong
and specific labeling was also observed at a number of
non-mitochondrial sites including various locations in
k i d n ey, such as on cell surface in distal tubules and
cortical collecting ducts, in condensing vacuoles, along
cell boundaries between adjoining cells, and in
endothelial cells lining capillaries in the glomerulus.
S u r face labeling due to mAspAT was also seen in
arteriolar endothelial cells and in lymphocytes. These
findings support the previous identification of mAspAT
as both a mitochondrial enzyme and a plasma membrane
protein. It is suggested that in accordance with its
established role in other cells and tissues, the surfa c e -
located mAspAT in kidney and endothelial cells is i nvo l ved in the fatty acid transport process. The duallocalization
of mAspAT, as well as a large number of
other mitochondrial proteins (viz. Hsp60, Hsp10,
Cytochrome c, TRAP-1 and P32 (gC1q-R)) in recent
studies, within both mitochondria and at various specific
extramitochondrial sites raises fundamental questions
about the role of mitochondria in cell structure and
function, and about the mechanisms that exist in normal
cells for protein translocation from mitochondria to other
compartments. These results have implications for the
role of mitochondria in apoptosis and different diseases.
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