Data Associated with 'Guanine Crystallization at Physiological pH'

Molecular organic crystals such as guanine are widely used by organisms for their remarkable optical properties. However, little is currently known about the mechanisms by which organisms control their formation, where efforts to elucidate these have been impeded by the very low solubility of these molecules in aqueous solutions at neutral pH. This creates significant challenges in crystallizing them under biologically-relevant conditions in the laboratory. Here, we introduce an enzymatic approach based on the purine metabolism process that yields significant quantities of guanine crystals in aqueous solution at neutral pH. The enzyme purine nucleoside phosphorylase (PNP) is used to continuously convert guanosine to guanine and generate supersaturation, and pure beta anhydrous guanine (β-AG) or alpha anhydrous guanine (α-AG) can be produced by changing the reagent concentrations or introducing stirring. Investigation of the reaction kinetics using high performance liquid chromatography (HPLC) and NMR reveals that the rate of change of supersaturation is crucial in determining the polymorph. This work bridges the gap between in vitro and biological crystallization and provides a facile means of studying the crystallization of biological molecules.