InterPro domain: IPR023468

Riboflavin is converted into catalytically active cofactors (FAD and FMN) by the actions of riboflavin kinase ( 2.7.1.26 ), which converts it into FMN, and FAD synthetase ( 2.7.7.2 ), 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 [ 1 ], the monofunctional FAD synthetase differs from its prokaryotic counterpart, and is instead related to the PAPS-reductase family [ 2 ]. 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 [ 3 ].

This entry represents riboflavin kinase, which occurs as part of a bifunctional enzyme or a stand-alone enzyme.

1. Ligand binding-induced conformational changes in riboflavin kinase: structural basis for the ordered mechanism. Biochemistry 42, 12532-8
2. Over-expression in Escherichia coli, purification and characterization of isoform 2 of human FAD synthetase. Protein Expr. Purif. 52, 175-81
3. A conserved domain in prokaryotic bifunctional FAD synthetases can potentially catalyze nucleotide transfer. Trends Biochem. Sci. 28, 9-12