bifunctional enzyme from E. coli which catalyzes second & third steps in biosynthesis of riboflavin; deamination of 2,5-diamino-6-ribosylamino-4(3H)pyrimidinone 5'-phosphate and reduction of 5-amino-6-ribosylamino-2,4(1H,3H) -pyrimidinedione 5'-phosphate to 5-amino-6-ribitylamino- 2,4(1H,3H)-pyrimidinedione 5'-phosphate