Enzyme - 3,4-dihydroxy-2-butanone-4-phosphate synthase

Alternative Name(s)
  • DHBP synthase.
  • L-3,4-dihydroxybutan-2-one-4-phosphate synthase.

Catalytic Activity

D-ribulose 5-phosphate = (2S)-2-hydroxy-3-oxobutyl phosphate + formate + H(+)



Reaction Mechanisms

    L-3,4-Dihydroxy-2-butanone-4-phosphate synthase catalyses the conversion of ribulose 5-phosphate to L-3,4-dihydroxy-2-butanone-4-phosphate (DHBP) and formate in riboflavin biosynthesis. The proposed mechanism shares features with many enzymes, including the sugar isomerases.

    A His-Asn dyad is central to the proposed mechanism of L-3,4-Dihydroxy-2-butanone-4-phosphate synthase. An initial enolisation step is mediated by Glu 185 acting as a general base to abstract the C3 proton in concert with the donation of a proton to the C2 carbonyl oxygen by His 147. Stabilisation of the enolate occurs via His 147, Asn 106 and Tyr 95. Dehydration is assisted by Cys 55 acting as a general acid. The enol is ketonised by an acid-base process with the C2 hydroxyl deprotonated by His 147 and a proton donated to C1 by Glu 185. A skeleton rearrangement is initiated by deprotonation of the C4 hydroxyl by Asp 30. Hydration by a magnesium-associated water follows with proton donation from His 147 yields the enolate intermediate, which binds to one magnesium only so that Glu 185 can deprotonate the C2 hydroxyl and the final product is generated by protonation by a magnesium-activated water.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    Asn Q60364 106 1snn 106
    Tyr Q60364 95 1snn 95
    Asp Q60364 30 1snn 30
    Cys Q60364 55 1snn 55
    Glu Q60364 185 1snn 185
    His Q60364 147 1snn 147

Reaction Parameters

  • Kinetic Parameters
    Organism KM Value [mM] Substrate Comment
    Salmonella enterica subsp. enterica serovar Typhimurium 0.116 D-ribulose 5-phosphate 37°C, pH 7.5, Vmax: 199 nmol/min/mg
    Streptococcus pneumoniae 0.181 D-ribulose 5-phosphate pH 7.5, 37°C
  • Temperature
    Organism Temperature Range Comment
    Streptococcus pneumoniae 5 - 55 activity range, profile overview. Highest activity at 33°C, while at 30°C and 37°C, the activity decreases sharply to approximately 15-30% of the activity at 33°C
  • pH
    Organism pH Range Comment
    Mycobacterium tuberculosis 5 - 9 enzyme loses activity below pH 5.0 and above pH 9.0
    Streptococcus pneumoniae 6 - 8 narrow optimum, no activity below or above, profile overview

Associated Proteins

Protein name Organism
Monofunctional riboflavin biosynthesis protein RIBA 2, chloroplastic Mouse-ear cress
3,4-dihydroxy-2-butanone 4-phosphate synthase Escherichia coli (strain K12)
Riboflavin biosynthesis protein RibBA Mycobacterium ulcerans (strain Agy99)
Probable bifunctional riboflavin biosynthesis protein RIBA 1, chloroplastic Rice
Probable bifunctional riboflavin biosynthesis protein RIBA 2, chloroplastic Rice