Mutation of Lys-120 and Lys-134 drastically reduces the catalytic rate of Cu,Zn superoxide dismutase

Lys-120 and Lys-134, located at the edge of the active site channel in most Cu,Zn superoxide dismutases, have been suggested to play a major role in steering the anionic substrate towards the catalytic copper ion. In this study, mutants of Xenopus laevis Cu,Zn superoxide dismutase have been engineered, with Lys-120 and Lys-134 changed into leucine and threonine, respectively, and their catalytic properties have been investigated by pulse radiolysis. Results obtained demonstrate that both residues decrease the catalytic rate by about 40%, in partial disagreement with previous brownian dynamics calculations, carried out on bovine Cu,Zn superoxide dismutase.