Oxaloacetate (OAA)

OAA is an intermediate in several important pathways, including gluconeogenesis, citric acid cycle, glyoxylate cycle, urea cycle, and amino acid metabolism (see here).

Oxaloacetate is formed in the glyoxylate, citric acid, and urea cycles as a result of catalysis by malate dehydrogenase:

L-Malate + NAD+ <=> Oxaloacetate + NADH + H+

In the reaction, hydrogens are transferred to NAD+, forming NADH + H+ . Oxaloacetate can be converted in the citric acid and glyoxylate cycles to citrate by addition of acetyl-CoA by the enzyme citrate synthase. In the urea cycle, oxaloacetate is transaminated by a transaminase to form aspartic acid.

> Oxaloacetate + Glutamate <-> Aspartate + -Ketoglutarate (catalyzed by SGOT)

Some of the enzymes that act on OAA include the following:

Pyruvate Carboxylase

PEPCK

Citrate Synthase

Malate Dehydrogenase

See also: Malate/Aspartate Shuttle, Transamination in Amino Acid Metabolism (from Chapter 20), Citric Acid Cycle Intermediates in Amino Acid Metabolism (from Chapter 21)

INTERNET LINKS:

> 1. Glyoxylate Cycle Metabolism

> 2. Citric Acid Cycle

> 3. Urea Cycle and Metabolism of Amino Groups