Biosynthetic pathway of citrinin in the filamentous fungus Monascus ruber as revealed by C-13 nuclear magnetic resonance

Carbon isotope distribution of [C-13]citrinin from Monascus ruber incubated with [C-13]acetate revealed that the biosynthesis of the toxin originated from a tetraketide, instead of a pentaketide as has been shown for Penicill ium and Aspergillus species. The production of polyketide red pigments and citrinin by M. ruber may therefore be regulated at the level of the tetrake tide branch point.