A decline in alpha-ketoglutarate dehydrogenase complex (KGDHC) activity has been associated
with neurodegeneration. Provision of succinyl-CoA by KGDHC is essential for generation
of matrix ATP (or GTP) by substrate-level phosphorylation catalyzed by succinyl-CoA
ligase. Here, we demonstrate ATP consumption in respiration-impaired isolated and
in situ neuronal somal mitochondria from transgenic mice with a deficiency of either
dihydrolipoyl succinyltransferase (DLST) or dihydrolipoyl dehydrogenase (DLD) that
exhibit a 20-48% decrease in KGDHC activity. Import of ATP into the mitochondrial
matrix of transgenic mice was attributed to a shift in the reversal potential of the
adenine nucleotide translocase toward more negative values due to diminished matrix
substrate-level phosphorylation, which causes the translocase to reverse prematurely.
Immunoreactivity of all three subunits of succinyl-CoA ligase and maximal enzymatic
activity were unaffected in transgenic mice as compared to wild-type littermates.
Therefore, decreased matrix substrate-level phosphorylation was due to diminished
provision of succinyl-CoA. These results were corroborated further by the finding
that mitochondria from wild-type mice respiring on substrates supporting substrate-level
phosphorylation exhibited approximately 30% higher ADP-ATP exchange rates compared
to those obtained from DLST+/- or DLD+/- littermates. We propose that KGDHC-associated
pathologies are a consequence of the inability of respiration-impaired mitochondria
to rely on "in-house" mitochondrial ATP reserves.-Kiss, G., Konrad, C., Doczi, J.,
Starkov, A. A., Kawamata, H., Manfredi, G., Zhang, S. F., Gibson, G. E., Beal, M.
F., Adam-Vizi, V., Chinopoulos, C. The negative impact of alpha-ketoglutarate dehydrogenase
complex deficiency on matrix substrate-level phosphorylation.