8-demethyl-8-formylriboflavin 5'-phosphate + A + H2O = 8-carboxy-8-demethylriboflavin 5'-phosphate + AH2 + H(+)
8-demethyl-8-formylriboflavin 5'-phosphate + a + h2o = 8-carboxy-8-demethylriboflavin 5'-phosphate + ah2 + h(+)