Studies of de novo Purine Biosynthetic Complexes in Living Cells

Abstract

Purines are synthesized in ten chemical steps catalyzed by six enzymes in eukaryotes. Studies in vitro have provided scant evidence for anticipated protein‐protein interactions that would enable substrate channeling and regulation of the metabolic flux. We have applied fluorescence microscopy to HeLa and human breast cancer cells and discovered that all six enzymes colocalize to form clusters in the cellular cytoplasm. The association and dissociation of these enzyme clusters can be regulated dynamically by changing the purine levels or by the addition of exogenous agents to the culture media. Collectively, the data provide strong evidence for the constitution of a multi‐enzyme complex, the purinosome, to carry out de novo purine biosynthesis in cells.