Riboflavin kinase

In enzymology, a riboflavin kinase (EC is an enzyme that catalyzes the chemical reaction

riboflavin kinase
Crystal structure of riboflavin kinase from Thermoplasma acidophilum.[1]
EC no.
CAS no.9032-82-0
IntEnzIntEnz view
ExPASyNiceZyme view
MetaCycmetabolic pathway
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO
Riboflavin kinase
PDB 1s4m EBI.jpg
crystal structure of flavin binding to fad synthetase from thermotoga maritina
Riboflavin kinase
ATP + riboflavin ADP + FMN

Thus, the two substrates of this enzyme are ATP and riboflavin, whereas its two products are ADP and FMN.

Riboflavin is converted into catalytically active cofactors (FAD and FMN) by the actions of riboflavin kinase (EC, which converts it into FMN, and FAD synthetase (EC, which adenylates FMN to FAD. Eukaryotes usually have two separate enzymes, while most prokaryotes have a single bifunctional protein that can carry out both catalyses, although exceptions occur in both cases. While eukaryotic monofunctional riboflavin kinase is orthologous to the bifunctional prokaryotic enzyme,[2] the monofunctional FAD synthetase differs from its prokaryotic counterpart, and is instead related to the PAPS-reductase family.[3] The bacterial FAD synthetase that is part of the bifunctional enzyme has remote similarity to nucleotidyl transferases and, hence, it may be involved in the adenylylation reaction of FAD synthetases.[4]

This enzyme belongs to the family of transferases, to be specific, those transferring phosphorus-containing groups (phosphotransferases) with an alcohol group as acceptor. The systematic name of this enzyme class is ATP:riboflavin 5'-phosphotransferase. This enzyme is also called flavokinase. This enzyme participates in riboflavin metabolism.

However, archaeal riboflavin kinases (EC in general utilize CTP rather than ATP as the donor nucleotide, catalyzing the reaction

CTP + riboflavin CDP + FMN [5]

Riboflavin kinase can also be isolated from other types of bacteria, all with similar function but a different number of amino acids.


The complete enzyme arrangement can be observed with X-ray crystallography and with NMR. The riboflavin kinase enzyme isolated from Thermoplasma acidophilum contains 220 amino acids. The structure of this enzyme has been determined X-ray crystallography at a resolution of 2.20 Å. Its secondary structure contains 69 residues (30%) in alpha helix form, and 60 residues (26%) a beta sheet conformation. The enzyme contains a magnesium binding site at amino acids 131 and 133, and a Flavin mononucleotide binding site at amino acids 188 and 195.

As of late 2007, 14 structures have been solved for this class of enzymes, with PDB accession codes 1N05, 1N06, 1N07, 1N08, 1NB0, 1NB9, 1P4M, 1Q9S, 2P3M, 2VBS, 2VBT, 3CTA, 2VBU, and 2VBV.


  1. ^ PDB: 3CTA​; Bonanno, J.B.; Rutter, M.; Bain, K.T.; Mendoza, M.; Romero, R.; Smith, D.; Wasserman, S.; Sauder, J.M.; Burley, S.K.; Almo, S.C. (2008). "Crystal structure of riboflavin kinase from Thermoplasma acidophilum". {{cite journal}}: Cite journal requires |journal= (help)
  2. ^ Osterman AL, Zhang H, Zhou Q, Karthikeyan S (2003). "Ligand binding-induced conformational changes in riboflavin kinase: structural basis for the ordered mechanism". Biochemistry. 42 (43): 12532–8. doi:10.1021/bi035450t. PMID 14580199.
  3. ^ Galluccio M, Brizio C, Torchetti EM, Ferranti P, Gianazza E, Indiveri C, Barile M (2007). "Over-expression in Escherichia coli, purification and characterization of isoform 2 of human FAD synthetase". Protein Expr. Purif. 52 (1): 175–81. doi:10.1016/j.pep.2006.09.002. PMID 17049878.
  4. ^ Srinivasan N, Krupa A, Sandhya K, Jonnalagadda S (2003). "A conserved domain in prokaryotic bifunctional FAD synthetases can potentially catalyze nucleotide transfer". Trends Biochem. Sci. 28 (1): 9–12. doi:10.1016/S0968-0004(02)00009-9. PMID 12517446.
  5. ^ Ammelburg M, Hartmann MD, Djuranovic S, Alva V, Koretke KK, Martin J, Sauer G, Truffault V, Zeth K, Lupas AN, Coles M (2007). "A CTP-Dependent Archaeal Riboflavin Kinase Forms a Bridge in the Evolution of Cradle-Loop Barrels". Structure. 15 (12): 1577–90. doi:10.1016/j.str.2007.09.027. PMID 18073108.

Further readingEdit

This article incorporates text from the public domain Pfam and InterPro: IPR015865