John Buchanan Began the Elucidation of the Synthesis of Purine $\beta$

Multiple Choice

John Buchanan began the elucidation of the synthesis of purine nucleotides by studying _______ excreted by pigeons fed isotopically labeled compounds.

A) "xanthine"
B) "hypoxanthine"
C) "uric acid"
D) " $\beta$ -alanine"
E) " $\beta$ -aminoisobutyrate"