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Using lipoate enantiomers and thioredoxin to study the mechanism of the 2‐oxoacid‐dependent dihydrolipoate production by the 2‐oxoacid dehydrogenase complexes
Author(s) -
Bunik V.,
Shoubnikova A.,
Loeffelhardt S.,
Bisswanger H.,
Borbe H.O.,
Follmann H.
Publication year - 1995
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(95)00904-n
Subject(s) - chemistry , mechanism (biology) , biochemistry , enantiomer , oxoglutarate dehydrogenase complex , dehydrogenase , enzyme , branched chain alpha keto acid dehydrogenase complex , stereochemistry , philosophy , epistemology
The thioredoxin‐catalyzed insulin reduction by dihydrolipoate was applied to study the 2‐oxoacid:lipoate oxidoreductase activity of 2‐oxoacid dehydrogenase complexes. The enzymatic and non‐enzymatic mechanisms of the transfer of reducing equivalents from the complexes to free lipoic acid (α‐lipoic acid, 6,8‐thiooctic acid) were distinguished using the high stereoselectivity of the complex enzymes to the R ‐enantiomer of lipoate. Unlike these enzymes, thioredoxin from E. coli exibited no stereoselectivity upon reduction with chemically obtained dihydrolipoate. However, coupled to the dihydrolipoate production by dehydrogenase complexes, the process was essentially sensitive both to the enantiomer used and the dihydrolipoyl dehydrogenase activity of the complexes. These results indicated the involvement of the third complex component, dihydrolipoyl dehydrogenase, in the 2‐oxoacid‐dependent dihydrolipoate formation. The implication of the investigated reaction for a connection between thioredoxin and the 2‐oxoacid dehydrogenase complexes in the mitochondrial metabolism are discussed.