2. Radioisotope tracer(放射同位素示踪 experiments revealed the origins of the atoms in the purine and pyrimidine rings Buchanan and Greenberg revealed this by feeding a variety of isotopically labeled compounds to pigeons(1940s) The atoms of the purine rings were found to be derived from formate, co2, Gly, Asp, and gIn The atoms of the pyrimidine rings were found to be derived from Asp, gIn and HCO3-2. Radioisotope tracer(放射同位素示踪) experiments revealed the origins of the atoms in the purine and pyrimidine rings • Buchanan and Greenberg revealed this by feeding a variety of isotopically labeled compounds to pigeons (1940s). • The atoms of the purine rings were found to be derived from formate, CO2 , Gly, Asp, and Gln. • The atoms of the pyrimidine rings were found to be derived from Asp, Gln and HCO3 -