2-ketoacid dehydrogenase complexes of Escherichia coli: stereospecificities of the three components for (R)-lipoate.
Stereospecificities of component enzymes in the pyruvate dehydrogenase complex and 2-ketoglutarate dehydrogenase complex from Escherichia coli for lipoate and dihydrolipoate are determined. Assays of the component enzymes using R,S-, R-, or S-lipoate or the enantiomers of dihydrolipoate show that only the R-enantiomers are substrates for these enzymes. Nonenzymatic reactions involving acetyl group transfer and coupled electron and acetyl group transfer between enantiomeric molecules of lipoate or/and dihydrolipoate proceed at significant rates. Coupled acetyl group and electron transfer from enzyme-bound acetyldihydrolipoyl moieties to free lipoate is also observed. The S-enantiomers are neither substrates nor inhibitors; however, products of S-enantiomers are slowly generated in enzymatic reactions owing to nonenzymatic reactions between enzyme-bound acetyldihydrolipoyl-groups and free S-lipoate or S-dihydrolipoate.
Yang
Y S
YS
Institute for Enzyme Research, Graduate School, University of Wisconsin, Madison 53705.
Frey
P A
PA
D000107:Acetylation; D004926:Escherichia coli / Q000201:enzymology*; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism*; D007658:Ketone Oxidoreductases / Q000378:metabolism*; D010084:Oxidation-Reduction; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism*; D013237:Stereoisomerism; D013379:Substrate Specificity; D008063:Thioctic Acid / Q000031:analogs & derivatives / Q000378:metabolism*
D011768:Pyruvate Dehydrogenase Complex; D008063:Thioctic Acid; C015144:dihydrolipoic acid; D007658:Ketone Oxidoreductases; D007655:Ketoglutarate Dehydrogenase Complex