Enzyme - L-lactate dehydrogenase (cytochrome)

Alternative Name(s)
  • L-lactate ferricytochrome c oxidoreductase.
  • Lactic acid dehydrogenase.
  • Cytochrome b2.

Catalytic Activity

(S)-lactate + 2 [Fe(III)cytochrome c] = 2 [Fe(II)cytochrome c] + 2 H(+) + pyruvate


FMN; Heme b.

Reaction Mechanism

    The flavo-cytochrome enzyme is a lactate dehydrogenase that catalyses the transfer of a hydride equivalent from its hydroxy acid substrate to the enzyme bound flavin, and thence to proteins of the mitochondrial electron transport chain via a bound cytochrome. The enzyme contains two domains, the flavin domain, capable of converting lactate to pyruvate by itself, and the heme domain which contains the prosthetic group involved in electron transfer from the reduced flavin to an acceptor cytochrome.

    The enzyme catalyses the oxidation of lactate to pyruvate. In the wild type enzyme the OH and CH bond cleavages in lactate are highly asynchronous. The lactate hydroxyl proton is abstracted by His 373 to form the alkoxide either early in the reaction or in a pre-equilibrium. The developing charge on the oxygen is stabilised by Tyr254. The hydride is then transferred to the flavin, forming pyruvate.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    Tyr P00175 334 1fcb 254
    Asp P00175 362 1fcb 282
    His P00175 453 1fcb 373
    Step Components

    overall reactant used, overall product formed, radical formation, proton transfer, radical termination, native state of cofactor regenerated, intermediate formation, aromatic bimolecular nucleophilic addition, bimolecular elimination, native state of enzyme regenerated, inferred reaction step, cofactor used, electron transfer, hydride transfer

    Step 1.

    His373 deprotonates the alcohol of the lactate which eliminates a hydride ion that is added to FAD.

    Step 2.

    A single electron is transferred from the FAD to the haem cofactor.

    Step 3.

    The haem cofactor transfers the electron to ferricytochrome c.

    Step 4.

    Water deprotonates the FAD, initiating the second single electron transfer from FAD to the haem cofactor.

    Step 5.

    The haem cofactor transfers the electron to ferricytochrome c.

    Step 6.

    Water deprotonates His373 in an inferred return step.


    The products of the reaction.

Reaction Parameters

There are no kinetic parameters information for this Enzyme

Associated Proteins

Protein name Organism
Cytochrome b2, mitochondrial Baker's yeast
Cytochrome b2, mitochondrial, putative Yeast
L-lactate dehydrogenase (Cytochrome) 3 Rhizobium sp. IE4771
L-lactate dehydrogenase LldA Rubrivivax gelatinosus (strain NBRC 100245 / IL144)
Cytochrome b2 mitochondrial Ceratocystis fimbriata f. sp. platani