Reconstitution of the ribonucleotide reductase enzyme from Ehrlich tumor cells

Ribonucleotide reductase from Ehrlich tumor cells was separated by chromatography on blue dextran/Sepharose into two protein fractions (Tris and Dye fractions). Neither fraction alone had reductase activity, but when combined, constituted an active enzyme system. Heat treatment of either fraction resulted in an inactive combination. The approximate molecular size of the active component of the Tris and Dye fractions was determined to be 5.7 S and 6.5 S, respectively, compared to 9 S for the intact enzyme. The Tris fraction was inactivated by hydroxylamine while the dye fraction was inactivated by pyridoxal phosphate/BH4-treatment. The inactivation of the Dye fraction was prevented by ATP. These data would indicate that the Tris and Dye fractions were comparable in function to the B2 and B1 proteins, respectively, of the Escherichia coli ribonucleotide reductase.