Thioredoxin elicits a new dihydrolipoamide dehydrogenase activity by interaction with the electron-transferring flavoprotein in Clostridium litoralis and Eubacterium acidaminophilum.
The glycine-utilizing bacterium Clostridium litoralis contained two enzyme systems for oxidizing dihydrolipoamide. The first one was found to be a genuine dihydrolipoamide dehydrogenase, present only in low amounts. This enzyme had the typical dimeric structure with a subunit molecular mass of about 53 kDa; however, it reacted with both NADP (Km 0.11 mM) and NAD (Km 0.5 mM). The reduction of pyridine nucleotides by dihydrolipoamide was the strongly preferred reaction. A second dihydrolipoamide-oxidizing enzyme system consisted of the interaction of two proteins, the previously described NADP(H)-dependent electron-transferring flavoprotein (D. Dietrichs, M. Meyer, B. Schmidt, and J. R. Andreesen, J. Bacteriol. 172:2088-2095, 1990) and a thioredoxin. This enzyme system was responsible for most of the dihydrolipoamide dehydrogenase activity in cell extracts. The thioredoxin did not bind to DEAE, was heat stable, and had a molecular mass of about 15 kDa. N-terminal amino acid analysis of the first 38 amino acid residues resulted in 38% homology to Escherichia coli thioredoxin and about 76% homology to a corresponding protein isolated from the physiologically close related Eubacterium acidaminophilum. The protein of the latter organism had a molecular mass of about 14 kDa and stimulated the low dihydrolipoamide dehydrogenase activity of the corresponding flavoprotein. By this interaction with NADPH-dependent flavoproteins, a new assay system for thioredoxin was established. A function of thioredoxin in glycine metabolism of some anaerobic bacteria is proposed.
Meyer
M
M
Institut für Mikrobiologie, Universität Göttingen, Federal Republic of Germany.
Dietrichs
D
D
Schmidt
B
B
Andreesen
J R
JR
D000595:Amino Acid Sequence; D003013:Clostridium / Q000201:enzymology*; D008058:Dihydrolipoamide Dehydrogenase / Q000302:isolation & purification / Q000378:metabolism*; D004579:Electron Transport / Q000187:drug effects; D044927:Electron-Transferring Flavoproteins; D004591:Electrophoresis, Polyacrylamide Gel; D005051:Eubacterium / Q000201:enzymology*; D005420:Flavoproteins / Q000302:isolation & purification / Q000502:physiology*; D008969:Molecular Sequence Data; D009249:NADP / Q000502:physiology; D012689:Sequence Homology, Nucleic Acid; D013879:Thioredoxins / Q000378:metabolism*
D044927:Electron-Transferring Flavoproteins; D005420:Flavoproteins; D013879:Thioredoxins; D009249:NADP; D008058:Dihydrolipoamide Dehydrogenase