Purification and characterization of branched chain alpha-ketoacid dehydrogenase from bovine liver mitochondria. J Biol Chem 1979 Jun 25;254(12):5522-6
Date
06/25/1979Pubmed ID
447664Scopus ID
2-s2.0-0018355912 (requires institutional sign-in at Scopus site) 62 CitationsAbstract
Branched chain alpha-ketoacid dehydrogenase (EC 1.2.4.3(4)) was solubilized and purified from bovine liver mitochondria for the first time. Decarboxylation of alpha-ketoisovalerate, alpha-keto-beta-methylvalerate, and alpha-ketoisocaproate was catalyzed by this multienzyme complex and this activity was co-purified for each substrate. Three enzymatic functions were contained in the complex including decarboxylation of the above ketoacids, transacylation of their simple acid derivatives, and reduction of NAD+ as an overall reaction. Product stoichiometry of these three reactions was 1 CO2:1 acyl-CoA:1 NADH. Activity depended upon the addition of thiamin pyrophosphate, CoASH, and NAD+ which were dissociable cofactors. Physically, two active forms of the enzyme complex were found: a 275,000-dalton unit and a 2 x 10(6)-dalton component. Both showed a characteristic flavin spectra and catalyzed all functions of the complex, implying that 10 small units aggregated into the larger unit. The soluble complex as visualized by electron microscopy had a diameter ranging from 12 to 24 nm corresponding to a molecular weight of 2 x 10(6). The size of the native membrane-bound component remains to be determined.
Author List
Danner DJ, Lemmon SK, Besharse JC, Elsas LJ 2ndMESH terms used to index this publication - Major topics in bold
Amino Acids, Branched-ChainAnimals
Cattle
Keto Acids
Ketone Oxidoreductases
Kinetics
Microscopy, Electron
Mitochondria, Liver
Molecular Weight
Multienzyme Complexes
Substrate Specificity