<p>Riboflavin is converted into catalytically active cofactors (FAD and FMN) by the actions of riboflavin kinase (<db_xref db="EC" dbkey="2.7.1.26"/>), which converts it into FMN, and FAD synthetase (<db_xref db="EC" dbkey="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 [<cite idref="PUB00030175"/>], the monofunctional FAD synthetase differs from its prokaryotic counterpart, and is instead related to the PAPS-reductase family [<cite idref="PUB00035657"/>]. 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 [<cite idref="PUB00010127"/>].</p><p>This entry represents riboflavin kinase, which occurs as part of a bifunctional enzyme or a stand-alone enzyme.</p> Riboflavin kinase