Malate

Malate is the ionized form of malic acid and a four-carbon intermediate in central metabolism. Plants can accumulate it in vacuoles, where it contributes to acidity and carbon storage.

Malic acid: Malic acid is a dicarboxylic acid whose conjugate base is malate. Malate is the deprotonated form of this acid, with their balance depending on pH.
Crassulacean acid metabolism: Crassulacean acid metabolism is a photosynthetic pathway that takes up carbon dioxide at night and uses it during the day. Its nighttime carbon fixation stores malate in vacuoles for daytime use.
Dicarboxylic acid: A dicarboxylic acid is an organic acid containing two carboxyl groups. Malic acid has two carboxyl groups, which can lose protons to form malate.
Citrate: Citrate is the ionized form of citric acid and a six-carbon intermediate in the tricarboxylic acid cycle. Both are organic-acid cycle intermediates, but citrate has six carbons and distinct pathway roles.
Tricarboxylic acid cycle: The tricarboxylic acid cycle is a series of reactions that oxidizes acetyl-CoA and transfers energy to electron carriers. Malate is one of its four-carbon intermediates.
CAM plants: CAM plants use crassulacean acid metabolism to reduce water loss in dry environments. Their daily malate cycle is a defining feature of this photosynthetic adaptation.
Oxaloacetate: Oxaloacetate is a four-carbon molecule that participates in the tricarboxylic acid cycle and related pathways. It interconverts with malate in a reaction central to cellular metabolism.
Fumarate: Fumarate is a four-carbon dicarboxylate formed by oxidation of succinate in the tricarboxylic acid cycle. It is another four-carbon cycle intermediate, but its reactions differ from malate’s.
Malate dehydrogenase: Malate dehydrogenase is an enzyme that interconverts malate and oxaloacetate while transferring electrons to or from NAD(H). It catalyzes a reversible reaction that consumes or produces malate.
C4 carbon fixation: C4 carbon fixation concentrates carbon dioxide around Rubisco through spatially separated reactions. C4 plants produce malate as a transport form of fixed carbon.

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