Ligand binding and protein dynamics in cupredoxins

A study conducted on the effect of temperature on the binding of nitric oxide to the azurin and halocyanin copper proteins shows that at temperatures less than 200 degrees kelvin the reaction is geminate recombination whose kinetics are non-exponential. The Gaussian distribution of enthalpy barriers defines the reaction in azurin while in halocyanin it defines only 97% of the energy. At temperatures above 200 degrees kelvin the reaction is bimolecular. The reaction in these cupredoxins is similar to the binding of ligands in other heme proteins.