About Us
Contact Us
Login to Protein Lounge!

Catabolic Pathways for Methionine, Isoleucine, Threonine and Valine

This image is a scaled-down version of the actual pathway image. It does not contain any links to the protein information pages.


The carbon skeletons of Methionine, Isoleucine, Threonine and Valine are degraded by pathways that yield Succinyl-CoA (Succinyl-Coenzyme A), an intermediate of the Citric Acid Cycle. Methionine donates its Methyl group to one of several possible acceptors through S-adenosylmethionine and three of its four remaining carbon atoms are converted to the Propionate of Propionyl-CoA, a precursor of Succinyl-CoA. Isoleucine undergoes transamination, followed by oxidative decarboxylation of the resulting Alpha-Keto Acid. The remaining five-carbon skeleton is further oxidized to Acetyl-CoA and Propionyl-CoA. Valine undergoes transamination and decarboxylation and then a series of oxidation reactions convert the remaining four carbons to Propionyl-CoA (Ref.1). In human tissues, Threonine is also converted in two steps to Propionyl-CoA. This is the primary pathway for Threonine degradation [...]


1.How coenzyme B12 radicals are generated: the crystal structure of methylmalonyl-coenzyme A mutase at 2 A resolution.
Mancia F, Keep NH, Nakagawa A, Leadlay PF, McSweeney S, Rasmussen B, Bosecke P, Diat O, Evans PR.
Structure. 1996 Mar 15; 4(3):339-50.
2.Pyridoxal enzymes: mechanistic diversity and uniformity.
Hayashi H.
J. Biochem. 1995 Sep; 118(3):463-73.
You can get all the details on this pathway through subscription