L-Malic Acid (Malate)

L-malate is an intermediate in the citric acid cycle, urea cycle, amino acid metabolism, the glyoxylate cycle, and shuttles across membranes of the cell (Figure 18.31).

In the citric acid cycle (and urea cycle), L-malate is produced by addition of water to the molecule fumarate catalyzed by the enzyme fumarate hydratase. D-Malate cannot be produced by the enzyme.

L-malate is converted to oxaloacetate by action of the enzyme malate dehydrogenase. NADH is another product of this reaction. The same reactions occur in the urea cycle as well.

In the glyoxylate cycle, L-malate is created by combining glyoxylate with acetyl-CoA in a reaction catalyzed by the enzyme malate synthase.

Malic enzyme provides yet another way to make L-malate.

See also: Oxaloacetate, Fumarate, Citrate Shuttle, Shuttling Electron Carriers into the Mitochondrion, Figure 15.11

INTERNET LINKS:

> 1. Glyoxylate Cycle Metabolism

> 2. Citric Acid Cycle

> 3. Urea cycle and Metabolism of Amino Groups