Enzymatic characterization of dihydrolipoamide dehydrogenase from Streptococcus pneumoniae harboring its own substrate

Anders P Håkansson, Alexander W Smith

Research output: Contribution to journalArticlepeer-review


This study describes the enzymatic characterization of dihydrolipoamide dehydrogenase (DLDH) from Streptococcus pneumoniae and is the first characterization of a DLDH that carries its own substrate (a lipoic acid covalently attached to a lipoyl protein domain) within its own sequence. Full-length recombinant DLDH (rDLDH) was expressed and compared with enzyme expressed in the absence of lipoic acid (rDLDH(-LA)) or with enzyme lacking the first 112 amino acids constituting the lipoyl protein domain (rDLDH(-LIPOYL)). All three proteins contained 1 mol of FAD/mol of protein, had a higher activity for the conversion of NAD(+) to NADH than for the reaction in the reverse direction, and were unable to use NADP(+) and NADPH as substrates. The enzymes had similar substrate specificities, with the K(m) for NAD(+) being approximately 20 times higher than that for dihydrolipoamide. The kinetic pattern suggested a Ping Pong Bi Bi mechanism, which was verified by product inhibition studies. The protein expressed without lipoic acid was indistinguishable from the wild-type protein in all analyses. On the other hand, the protein without a lipoyl protein domain had a 2-3-fold higher turnover number, a lower K(I) for NADH, and a higher K(I) for lipoamide compared with the other two enzymes. The results suggest that the lipoyl protein domain (but not lipoic acid alone) plays a regulatory role in the enzymatic characteristics of pneumococcal DLDH.

Original languageEnglish
Pages (from-to)29521-30
Number of pages10
JournalJournal of Biological Chemistry
Issue number40
Publication statusPublished - 2007 Oct 5

Subject classification (UKÄ)

  • Infectious Medicine
  • Cell and Molecular Biology

Free keywords

  • Dihydrolipoamide Dehydrogenase
  • Flavins
  • Kinetics
  • Models, Chemical
  • NAD
  • Protein Binding
  • Protein Structure, Tertiary
  • Pyruvate Dehydrogenase Complex
  • Recombinant Proteins
  • Sequence Analysis, DNA
  • Streptococcus pneumoniae
  • Substrate Specificity
  • Sulfhydryl Compounds
  • Thioctic Acid


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