Precursor to metabolite: Riboflavin to FMN

Riboflavin is converted to FMN by riboflavin kinase.

The pair

Riboflavin — Vitamin B2; precursor to the flavin cofactors FMN and FAD.
FMN — Riboflavin-derived redox cofactor; accepts electrons in mitochondrial complex I and other flavoprotein reactions.