The Biosynthesis of Purine Nucleotides de Nova in the Rabbit Reticulocyte in Vitro*

The mature rabbit erythrocyte has been shown to be incapable of synthesizing de novo the purine portions of adenosine triphosphate and of guanosine triphosphate, in vitro (2). It is able, however, to carry out the final steps of this pathway from sodium formate and 5-amino-1-ribosyl-4-imidazolecarboxamide, a finclmg which suggests that a portion of the over-all enzymatic sequence is lost during the maturation process (2, 3). The study of the metabolic capacities of mammalian erythrocytes at various stages in their life span has now been extended to a consideration of the ability of rabbit reticulocytes to synthesize purine nucleotides, in vitro. The reticulocyte differs from the mature erythrocyte in several respects: it possesses a reticulum which in all likelihood is ribonucleoprotein and which is lost during maturation, it has an intact tricarboxylic acid cycle and electron transport system (4), and it can synthesize heme (5) and globin (6, 7). The studies which are reported in this paper demonstrate that the rabbit reticulocyte, in contrast to the mature erythrocyte, is able to synthesize, de novo, the purine portions of adenosine triphosphate and guanosine triphosphate, in vitro.