Oxaloacetate.

Malate dehydrogenase reduces oxaloacetate to malate while oxidising NADH back to NAD+. Supplying oxaloacetate therefore acts on the same cytosolic NAD+/NADH ratio that NAD itself sets.

Nicotinamide riboside raises the total NAD pool, while oxaloacetate shifts the existing pool toward the oxidised NAD+ form by accepting electrons from NADH. The two act on different halves of the same cofactor system.

NMN feeds the salvage route that builds total NAD, and oxaloacetate consumes NADH to leave more of that pool in the NAD+ state. Supply and redox balance are separate levers on one cofactor.

Aspartate aminotransferase interconverts oxaloacetate and aspartate in one step, so each is the immediate precursor of the other. The malate-aspartate shuttle runs on exactly this exchange.

Glutamate donates its amino group to oxaloacetate to yield aspartate and alpha-ketoglutarate. Glutamate availability sets how readily oxaloacetate moves into the amino acid pool rather than staying in the citric acid cycle.

Malate and oxaloacetate sit one reversible step apart on malate dehydrogenase, so the two interconvert according to the local NAD+/NADH ratio. Supplying both loads the same segment of the cycle from either side.

Pyruvate carboxylase is a biotin-dependent enzyme that carboxylates pyruvate to oxaloacetate. Biotin status governs how much oxaloacetate the body can generate on its own.

Every aminotransferase reaction, including the aspartate and oxaloacetate exchange, carries pyridoxal-5-phosphate as its prosthetic group. Without adequate B6 the transamination arm of oxaloacetate handling slows.

Citrate synthase condenses oxaloacetate with acetyl-CoA to open the citric acid cycle. Acetyl-L-carnitine can hand acetyl groups to the mitochondrial acetyl-CoA pool, so the two supply opposite halves of the same condensation.

Lipoic acid is the covalently bound cofactor of pyruvate dehydrogenase, the complex that generates the acetyl-CoA oxaloacetate condenses with. Adequate lipoate keeps acetyl-CoA arriving as oxaloacetate is supplied.

Pyruvate carboxylase carries a tightly bound divalent metal, manganese in the human enzyme, alongside its biotin group when it builds oxaloacetate from pyruvate. Manganese status therefore sits on the endogenous supply route.

Pyruvate carboxylase uses Mg-ATP to carboxylate pyruvate to oxaloacetate, and phosphoenolpyruvate carboxykinase uses Mg-GTP to take oxaloacetate the other way. Both reactions need magnesium bound to the nucleotide, not free. Adequate magnesium is a condition for oxaloacetate turnover rather than an additive effect on top of it.

Malate dehydrogenase interconverts malate and oxaloacetate using NAD as the electron acceptor, and the equilibrium sits far toward malate unless NAD is regenerated. Niacin is a dietary precursor of NAD through the Preiss-Handler route. The link is a cofactor supply relationship, not a claim that niacin raises oxaloacetate.

Malate dehydrogenase moves carbon between malate and oxaloacetate in both directions depending on the NAD to NADH ratio. Malate is the more stable of the pair in solution, which is why malate salts appear on labels far more often. The two occupy adjacent positions in the same cycle rather than doing different jobs.

Aspartate aminotransferase exchanges an amino group between aspartate and alpha-ketoglutarate to give oxaloacetate and glutamate, and it runs freely in both directions. The two keto acids are therefore linked in a single equilibrium. Supplying one influences the nitrogen handling of the pair rather than adding an independent effect.

Pyruvate carboxylase adds a carboxyl group from bicarbonate to pyruvate to produce oxaloacetate, the reaction that keeps the cycle topped up when intermediates are drained for biosynthesis. Oxaloacetate can also lose that carboxyl group non-enzymatically and revert to pyruvate, which is one reason the free acid is unstable in solution. Cell work has described the two as a linked metabolic axis.

Succinate dehydrogenase sits in both the citric acid cycle and the electron transport chain, passing electrons from succinate to the coenzyme Q pool. Oxaloacetate binds tightly at the succinate site and slows that step, a long-described regulatory brake. This is enzyme-level pharmacology measured in isolated mitochondria, not an observed interaction between two capsules.

Riboflavin is the precursor of FAD, which is covalently bound in succinate dehydrogenase and required for flux around the segment of the cycle that regenerates oxaloacetate from succinate. Without adequate flavin the cycle stalls upstream of oxaloacetate. This is cofactor supply, described at the level of the enzyme.

Citrate synthase joins acetyl-CoA to oxaloacetate to make citrate, the committed first step of the cycle. Pantothenic acid is the backbone of coenzyme A, so it sets the availability of the partner substrate. Oxaloacetate without an acetyl donor cannot enter the cycle.

Thiamine pyrophosphate drives the decarboxylation that turns pyruvate into acetyl-CoA, which is the substrate oxaloacetate condenses with. The same cofactor is needed at the alpha-ketoglutarate step further round the cycle. Thiamine status therefore governs whether added oxaloacetate has anything to react with.

Glutamine is deamidated to glutamate and transaminated or deaminated to alpha-ketoglutarate, which travels round the cycle to oxaloacetate. It is the dominant route by which cells replenish cycle carbon from an amino acid. The two enter the same pool at different points.

Pyruvate carboxylase transfers a carboxyl group from bicarbonate through a biotin arm onto pyruvate to form oxaloacetate. Bicarbonate concentration is normally set by carbonic anhydrase and respiratory control rather than by intake. Whether an oral bicarbonate dose changes this reaction in any meaningful way has not been shown, so read the link as biochemical context.

The free acid decarboxylates and oxidises readily, so commercial anhydrous enol-oxaloacetate is typically blended with ascorbic acid and kept dry and cool. The role of the ascorbate is to protect the material in the container, not to change what happens in the body. This is a manufacturing pairing.