Ferredoxin-dependent oxidative decarboxylases of Halobacterium salinarum

Two key enzymatic steps in central metabolism are the conversion of pyruvate to acetyl-CoA and of alpha-ketoglutarate to succinyl-CoA. These enzymatic reactions result in oxidative decarboxylation of the substrate. In Halobacterium salinarum and many archaea these are catalyzed by ferredoxin-dependent protein complexes while in Escherichia coli and most bacteria and eukaryotes these are catalyzed by lipoamide-dependent enzyme complexes.

I. Pyruvate dehydrogenase (ferredoxin)

Transcription unit porAB, which encodes for the pyruvate dehydrogenase (graphic generated by HaloLex).

Physiological role:

  • Pyruvate dehydrogenase converts pyruvate to acetyl-CoA which is then completely oxidyzed through the citric acid cycle.

Reaction catalyzed:

  • pyruvate + HSCoA + fdx(ox) --> acetyl-CoA + CO2 + fdx(red)

Protein complex:

  • Pyruvate dehydrogenase is a heterotetramer.

Subunits:

  • alpha chain: porA OE2623R PIR:S22396

  • beta chain: porB OE2622R PIR:S22397

Genes:

  • the genes porA-porB form a transcription unit.

Coenzymes and redox partners:

  • ferredoxin fdx OE4217R

  • coenzyme A

  • thiamine pyrophosphate

Experimental data:

  • The protein was purified and its catalytic properties were determined.

  • The molecular weight of the protein complex and its subunits as well as the amino acid composition was determined.

  • Protein sequencing of the N-terminus and of internal peptides was achieved.

  • The presence of the coenzyme thiamine pyrophosphate and the absence of the coenzyme lipoamide was verified.

References:

  • W. Plaga, F. Lottspeich, D. Oesterhelt:
    Improved Purification, Crystallization and Primary Structure of Pyruvate:Ferredoxin Oxidoreductase from Halobacterium halobium.
    Eur. J. Biochem. 205, 391-397 (1992)
  • L. Kerscher, D. Oesterhelt:
    Purification and Properties of Two 2-Oxoacid:Ferredoxin Oxidoreductases from Halobacterium halobium.
    J. Biochem. 116, 587-594 (1981)
  • L. Kerscher, D. Oesterhelt:
    The Catalytic Mechanism of 2-Oxoacid:Ferredoxin Oxidoreductases from Halobacterium halobium: One-Electron Transfer at two Distinct Steps of the Catalytic Cycle.
    Eur. J. Biochem. 116, 595-600 (1981)

II. Alpha-ketoglutarate dehydrogenase (ferredoxin)

Transcription unit korAB, which encodes for the alpha-ketoglutarate dehydrogenase (graphic generated by HaloLex).

Physiological role:

  • alpha-detoglutarate dehydrogenase is one step of the citric acid cycle.

Reaction catalyzed:

  • alpha-ketoglutarate + HSCoA + fdx(ox) --> succinyl-CoA + CO2 + fdx(red)

Subunits:

Genes:

  • the genes korA-korB form a transcription unit.

Coenzymes and redox partners:

  • ferredoxin fdx OE4217R
  • coenzyme A
  • thiamine pyrophosphate

Experimental data:

  • The protein was purified and its catalytic properties were determined.
  • The molecular weight of the protein complex and its subunits as well as the amino acid composition was determined.
  • The presence of the coenzyme thiamine pyrophosphate and the absence of the coenzyme lipoamide was verified.
  • The genes for the subunits were cloned and sequenced.

References

  • L. Kerscher, D. Oesterhelt:
    Purification and Properties of Two 2-Oxoacid:Ferredoxin Oxidoreductases from Halobacterium halobium.
    J. Biochem. 116, 587-594 (1981)
  • L. Kerscher, D. Oesterhelt:
    The Catalytic Mechanism of 2-Oxoacid:Ferredoxin Oxidoreductases from Halobacterium halobium: One-Electron Transfer at two Distinct Steps of the Catalytic Cycle.
    Eur. J. Biochem. 116, 595-600 (1981)
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