malate

Malate refers to the malate ion, the conjugate base of malic acid, as well as salts and esters derived from malic acid. Malic acid is a dicarboxylic acid with the formula C4H6O5; at physiological pH the deprotonated form, malate, carries a negative charge (commonly −2).

In biology, malate is an intermediate of cellular energy metabolism. It is produced from fumarate by fumarase in the citric acid cycle and is then oxidized to oxaloacetate by malate dehydrogenase, generating NADH for energy production. The malate–aspartate shuttle moves reducing equivalents into mitochondria by transferring malate into the mitochondrial matrix and regenerating NAD+. In gluconeogenesis, oxaloacetate derived from malate can be converted to phosphoenolpyruvate for glucose synthesis.

In plants, malate participates in carbon and osmotic regulation. It can be synthesized in the cytosol and stored in vacuoles, contributing to osmotic balance and stress responses. In CAM and C4 photosynthesis, malate functions as a carbon storage and transport form, being decarboxylated to release CO2 for fixation in the Calvin cycle.

Malate salts, such as calcium malate and magnesium malate, are used in agriculture and nutrition and are marketed as dietary supplements and food additives to improve mineral delivery and acidity regulation. In fermentation, malolactic fermentation converts malate to lactate and CO2, reducing acidity in products like wine.

Overall, malate is a versatile metabolite linking energy production, carbon metabolism, and cellular pH and osmotic regulation across organisms.