N-Acetylaspartate Synthesis as a Thermodynamic Relief Mechanism for Mitochondrial Aspartate Aminotransferase
- 1Biophysics Graduate Program, The Ohio State University
Abstract
N-acetylaspartate (NAA) is the most abundant neuron-enriched acetylated metabolite in the mammalian brain, but its metabolic purpose remains unresolved. We developed a simplified kinetic model of mitochondrial aspartate metabolism to test whether NAA synthesis by aspartate N-acetyltransferase (ASPNAT) acts as a thermodynamic relief valve for mitochondrial aspartate aminotransferase (AAT) under the low-oxaloacetate (OAA) conditions expected in neuronal mitochondria. In the mitochondrial-compartment model, ASPNAT lowered steady-state mitochondrial aspartate from 141 to 105 M and increased net forward AAT flux by 30.9%. The relative AAT-relief effect was largest when OAA and aspartate-glutamate carrier 1 (AGC1/Aralar1)-mediated export were both low, whereas acetyl-CoA availability controlled the substrate-supported capacity for NAA synthesis. That places the relief effect in a narrow regime where product removal matters most. ASPNAT titration produced a graded, concentration-dependent response rather than a binary on/off switch. Energetic comparisons showed that the gain in AAT-linked support comes at a modest acetyl-CoA cost, which makes NAA synthesis easier to sustain in carbon-replete states than in carbon-poor ones. Some studies have suggested a secondary cytoplasmic site of NAA synthesis, and we therefore examined how the network response changed with a change in ASPNAT topology. Mitochondrial matrix ASPNAT increased forward AAT flux by 53.32%, whereas cytoplasmic ASPNAT decreased ASPNAT flux by 17.8%. Allowing OAA to vary preserved the positive ASPNAT-dependent relief of AAT flux, but because this simplified extension produced unrealistically low absolute fluxes, it is interpreted as a robustness check on the direction of the mechanism rather than as a prediction of physiological metabolic rates. These results suggest that ASPNAT can serve as an auxiliary matrix-aspartate sink when the AAT node is product-limited.
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BibTeX
@misc{puthillathu2026nacetylaspartate,
title = {{N-Acetylaspartate Synthesis as a Thermodynamic Relief Mechanism for Mitochondrial Aspartate Aminotransferase}},
author = {N. Puthillathu and J. R. Moffett and B. S. Slusher and A. M. A. Namboodiri},
howpublished = {bioRxiv},
year = {2026},
month = jun,
doi = {10.64898/2026.06.29.735215},
url = {https://www.biorxiv.org/content/10.64898/2026.06.29.735215v2},
note = {CC0},
}
RIS
TY - UNPB
TI - N-Acetylaspartate Synthesis as a Thermodynamic Relief Mechanism for Mitochondrial Aspartate Aminotransferase
AU - N. Puthillathu
AU - J. R. Moffett
AU - B. S. Slusher
AU - A. M. A. Namboodiri
PY - 2026
DA - 2026/06/29
PB - bioRxiv
DO - 10.64898/2026.06.29.735215
UR - https://www.biorxiv.org/content/10.64898/2026.06.29.735215v2
AB - N-acetylaspartate (NAA) is the most abundant neuron-enriched acetylated metabolite in the mammalian brain, but its metabolic purpose remains unresolved. We developed a simplified kinetic model of mitochondrial aspartate metabolism to test whether NAA synthesis by aspartate N-acetyltransferase (ASPNAT) acts as a thermodynamic relief valve for mitochondrial aspartate aminotransferase (AAT) under the low-oxaloacetate (OAA) conditions expected in neuronal mitochondria. In the mitochondrial-compartment model, ASPNAT lowered steady-state mitochondrial aspartate from 141 to 105 M and increased net forward AAT flux by 30.9%. The relative AAT-relief effect was largest when OAA and aspartate-glutamate carrier 1 (AGC1/Aralar1)-mediated export were both low, whereas acetyl-CoA availability controlled the substrate-supported capacity for NAA synthesis. That places the relief effect in a narrow regime where product removal matters most. ASPNAT titration produced a graded, concentration-dependent response rather than a binary on/off switch. Energetic comparisons showed that the gain in AAT-linked support comes at a modest acetyl-CoA cost, which makes NAA synthesis easier to sustain in carbon-replete states than in carbon-poor ones. Some studies have suggested a secondary cytoplasmic site of NAA synthesis, and we therefore examined how the network response changed with a change in ASPNAT topology. Mitochondrial matrix ASPNAT increased forward AAT flux by 53.32%, whereas cytoplasmic ASPNAT decreased ASPNAT flux by 17.8%. Allowing OAA to vary preserved the positive ASPNAT-dependent relief of AAT flux, but because this simplified extension produced unrealistically low absolute fluxes, it is interpreted as a robustness check on the direction of the mechanism rather than as a prediction of physiological metabolic rates. These results suggest that ASPNAT can serve as an auxiliary matrix-aspartate sink when the AAT node is product-limited.
ER -