Role of protein X in the function of the mammalian pyruvate dehydrogenase complex.
Two lipoyl-bearing subunits--the dihydrolipoyl transacetylase and protein X--form the core of the mammalian pyruvate dehydrogenase complex. Selective removal of the lipoyl domain of protein X results in loss in the activity of the complex with a relationship suggesting the involvement of the lipoyl domain of protein X in a key but not rate limiting step. The dihydrolipoyl dehydrogenase component markedly reduces both the cleavage of protein X and the loss in activity. Using a microplate binding assay, we demonstrate that the lipoyl domain of protein X and the transacetylase component contribute to the binding of the dihydrolipoyl dehydrogenase component. These roles of protein X in the catalytic function and organization of the complex require new reactions and afford an explanation for the unusual stoichiometry of dihydrolipoyl dehydrogenase dimers in the complex.
Gopalakrishnan
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Department of Biochemistry, Kansas State University, Manhattan 66506.
Rahmatullah
M
M
Radke
G A
GA
Powers-Greenwood
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S
Roche
T E
TE
D000818:Animals; D001665:Binding Sites; D002417:Cattle; D004579:Electron Transport; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D010455:Peptides / Q000378:metabolism / Q000502:physiology*; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism / Q000502:physiology*; D013329:Structure-Activity Relationship
D010455:Peptides; D011768:Pyruvate Dehydrogenase Complex; C489061:pyruvate dehydrogenase complex component X, Bos taurus