Subsystem: Valine degradation

This subsystem's description is:

The catabolism of L-valine involves its conversion via 2-keto-isovalerate to isobutyryl-CoA, which is desaturated to form the alpha,beta-unsaturated thioester methylacrylyl-CoA. Hydration to 3-hydroxy-isobutyryl-CoA and thioester hydrolysis forms the diffusible and transportable compound 3-hydroxy-isobutyrate. Finally, this beta-hydroxy acid is oxidized to methylmalonate-semialdehyde and thioesterified to form propionyl-CoA.

The first two steps in BCAA (Branched-Chain Alpha-keto Acid) catabolism are common to the three BCAAs. BCAT catalyzes transamination of BCAAs, which is a reversible reaction to form BCKAs, and the BCKDH complex catalyzes the oxidative decarboxylation of BCKAs, an irreversible reaction. Since the BCKDH complex commits BCAAs to degradation and the BCKDH complex is subject to regulation by covalent modification, it is believed that the BCKDH complex catalyzes the rate-limiting step in the overall catabolism of the BCAAs.

The BCKDH complex is regulated by a phosphorylation/dephosphorylation cycle. BCKDH kinase is responsible for inactivation of the complex by phosphorylation of the E1{alpha}-subunit of the complex, and BCKDH phosphatase is responsible for activation of the complex by dephosphorylation of E1{alpha}.
Many reports suggest that the BCKDH kinase plays an important role in the regulation of the complex activity. The BCKDH phosphatase undoubtedly performs a significant role in the regulation of BCKDH complex activity, but little is known about the phosphatase, although it has been purified from bovine kidney.

======VARIANT CODES:=============================

1.0 - All genes of Valine degradation pathway are present;

1.x - Valine degradation pathway with missing genes(often they are the components of Branched-chain alpha-keto acid dehydrogenase complex and there is a annotation problem - conflict with other dehydrogenase complexes)

2.0 - Isobutyryl-CoA precursor goes straight to Branched-chain fatty acids biosynthesis ( as in Listeria)

-1 - No Valine degradation pathway

For more information, please check out the description and the additional notes tabs, below

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