Riboflavin is converted into catalytically active cofactors (FAD and FMN) by the actions of riboflavin kinase (EC126.96.36.199), which converts it into FMN, and FAD synthetase (EC188.8.131.52), 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, the monofunctional FAD synthetase differs from its prokaryotic counterpart, and is instead related to the PAPS-reductase family. 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.
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.
^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".
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^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. PMID17049878.
^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. PMID12517446.
Solovieva IM, Tarasov KV, Perumov DA (February 2003). "Main physicochemical features of monofunctional flavokinase from Bacillus subtilis". Biochemistry (Mosc.)68 (2): 177–81. PMID12693963.
Solovieva, I.M.; Kreneva, R.A.; Leak, D.J.; Perumov, D. A. (January 1999). "The ribR gene encodes a monofunctional riboflavin kinase which is involved in regulation of the Bacillus subtilis riboflavin operon". Microbiology145: 67–73. doi:10.1099/13500872-145-1-67. PMID10206712.