USE OF ISOTOPES IN STUDIES OF HEMOGLOBIN FORMATION

Isotopes of a number of chemical elements are now used as "tracers" for studying the mechanism and site of formation of substances in the animal organism. Investigations over the past five years which have elucidated the biosynthesis of creatine may be cited as an example. Recent work in the biosynthesis of hemoglobin is further evidence of the value of this experimental approach. The iron of the hemoglobin molecule is derived from either dietary iron or, apparently preferentially, from the destroyed red cell itself. The question of the formation of the porphyrin and the globin portions has remained unanswered until recently. The fact that the porphyrins may be synthesized in the body was clearly demonstrated in 1939 in rats fed porphyrin-low diets.¹ The globin moiety has been generally assumed to be derived from dietary protein. Using isotopic nitrogen (nitrogen 15) investigators at Columbia University² have found that the simple