The role of arginine residues at enzyme active sites. The interaction between guanidinium ions and p-nitro-phenyl phosphate and its effect on the rate of hydrolysis of the ester.

In alcoholic solutions a relatively strong complex forms among two guanidinium ions and one p-nitrophenylphosphate dianion. The effect of this complex formation on the hydrolysis of the ester is to lower the rate by a factor of 4 in solutions containing 1 M guanidine hydrochloride when compared with solutions of the same total ionic strength containing no guanidinium ion. It is therefore suggested that, for the enzymatically catalyzed hydrolysis of phosphate compounds going via the formation of a metaphosphate intermediate, the role of any arginine residues at the active site is primarily one of binding and positioning the substrate.