Alanine Metabolism

Alanine is most commonly produced by the reductive amination of pyruvate via alanine transaminase. This reversible reaction involves the interconversion of alanine and pyruvate, coupled to the interconversion of alpha-ketoglutarate (2-oxoglutarate) and glutamate. Because transamination reactions are readily reversible and pyruvate is widespread, alanine can be easily formed in most tissues. Another route to the production of alanine is through the enzyme called alanine-glyoxylate transaminase. This reaction involves the interconversion of alanine and pyruvate, coupled to the interconversion of glyoxylate and glycine. Once synthesized, alanine can be coupled to alanyl tRNA via alanyl-tRNA synthetase and used by the body in protein synthesis. Alanine constitutes about 8% of human proteins. Under fasting conditions, alanine, derived from protein breakdown, can be converted to pyruvate and used to synthesize glucose via gluconeogenesis in the liver. Alternately, alanine, after conversion to pyruvate, can be fully oxidized via the TCA cycle in other tissues.

References

1. Lehninger, A.L. (2005) Lehninger principles of biochemistry (4 ^th ed.). New York: W.H Freeman.
2. Salway, J.G. (2004) Metabolism at a glance (3 ^rd ed.). Alden, Mass. : Blackwell Pub.