Preparation of Flavocoenzyme Isotopologues by Biotransformation of Purines.

Isotope-labeled flavins are crucial reporters for many biophysical studies of flavoproteins. A purine-deficient Escherichia coli strain engineered for expression of the ribAGH genes of Bacillus subtilis converts isotope-labeled purine supplements into the riboflavin precursor, 6,7-dimethyl-8-ribityllumazine, with yields up to 40%. The fermentation products can subsequently be converted into isotope-labeled riboflavin and the cognate flavocoenzymes, FMN and FAD, by in vitro biotransformation with better than 90% yield. Using this approach, more than 100 single or multiple 13C-, 15N-, 17O-, and 18O-labeled isotopologues of these cofactors and ligands become easily accessible, enabling advanced ligand-based spectroscopy of flavoproteins and lumazine receptor proteins at unprecedented resolution. [ABSTRACT FROM AUTHOR]