Insight into the thermodynamic and catalytic features of NiSOD related metallopeptides

Abstract

The most recently discovered superoxide dismutase enzymes, NiSODs, contain nickel in their active center. This paper surveys the most relevant recent results in this field. Literature data confirm that designated Ni-containing metallopeptides are appropriate mimics of NiSOD. By varying the amino acid sequence of the binding hook, it was unequivocally confirmed that the dismutase activity is related to the coordination of cysteine moieties to Ni via the thiolate groups. While these metallopeptides are essential in modeling the structure, and electronic properties of NiSOD enzymes, their redox stability is not satisfactory to deliver sustained dismutase activity. The redox degradation of the model compounds is kinetically coupled with the dismutation cycle and the conventional first-order approach cannot be used for the interpretation of the decay of O2–•. For the very same reason, the use of the McCord-Fridovich assay is of limited value in these systems. Arguments are presented to demonstrate that direct kinetic studies, utilizing the sequential stopped-flow method, are required for studying the dismutation process under real catalytic conditions.