Malate (malic acid)

An important citric acid cycle intermediate. Via the malate-aspartate shuttle, malate carries electrons in the form of NADH from the cytoplasm into the mitochondria.

What malate does in the body

Malate is formed in the citric acid cycle from fumarate. Malate dehydrogenase converts it with NAD⁺ into oxaloacetate and passes electrons on to the respiratory chain as NADH; oxaloacetate then takes up the next acetyl-CoA, and the cycle starts again. Malate is also a means of transport: in the malate-aspartate shuttle it carries the electrons of the NADH produced in glycolysis in the cytoplasm across the inner mitochondrial membrane, which NADH itself cannot cross. Exported into the cytoplasm, malate serves the liver as starting material for making new glucose, and via malic enzyme it supplies NADPH for building fatty acids.

Low malate – what happens in the body?

When little malate is present, less oxaloacetate is formed as well; acetyl-CoA then finds a partner less easily, and the citric acid cycle turns more slowly. At the same time, the malate-aspartate shuttle can move fewer electrons from the cytoplasm into the mitochondria: NADH builds up in the cytoplasm, and more pyruvate is converted into lactate. Less malate is formed when the preceding steps of the cycle run more slowly or intermediates are drawn off to build amino acids and glucose.

High malate – what happens in the body?

A raised value can show that malate is being processed into oxaloacetate more slowly. Malate dehydrogenase needs NAD⁺, which is made from niacin; when NADH builds up because the respiratory chain is taking up fewer electrons, this step slows down and malate accumulates. The citric acid cycle and energy production in the mitochondria then run at a reduced pace. More malate is also produced when a lot of fumarate flows in from the urea cycle and amino acid breakdown, and malic acid from fruit and fruit juices can also contribute to the value.

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