The first is a two component regulatory system that senses the presence of ethanolamine and the second mechanism is a AdoCbl riboswitch that senses the presence of AdoCbl, a cofactor needed for the breakdown of ethanolamine.
Factor I requires a C3b-binding protein cofactor such as complement factor H, CR1, or Membrane Cofactor of Proteolysis (MCP or CD46)
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CFHR5 (Complement Factor H-Related protein 5) is able to bind to act as a cofactor for factor I, has decay accelerating activity and is able to bind preferentially to C3b at host surfaces.
C4BP accelerates decay of C3-convertase and is a cofactor for serine protease factor I which cleaves C4b and C3b.
ETFs are heterodimeric proteins composed of an alpha and beta subunit (ETFA and ETFB), and contain an FAD cofactor and AMP.
The spectroscopic properties of the flavin cofactor make it a natural reporter for changes occurring within the active site; this makes flavoproteins one of the most-studied enzyme families.
Kuvan (trade name for the cofactor tetrahydrobiopterin in a pill form)
IFRD1 is a positive cofactor of MyoD, as it cooperates with MyoD at inducing the transcriptional activity of MEF2C (by displacing HDAC4 from MEF2C); moreover IFRD1 also represses the transcriptional activity of NF-κB, which is known to inhibit MyoD mRNA accumulation.