Nickel-based Enzyme Systems

Abstract

Of the eight known nickel enzymes, all but glyoxylase I catalyze the use and/or production of gases central to the global carbon, nitrogen, and oxygen cycles. Nickel appears to have been selected for its plasticity in coordination and redox chemistry and is able to cycle through three redox states (1+, 2+, 3+) and to catalyze reactions spanning approximately 1.5 V. This minireview focuses on the catalytic mechanisms of nickel enzymes, with an emphasis on the role(s) of the metal center. The metal centers vary from mononuclear to complex metal clusters and catalyze simple hydrolytic to multistep redox reactions.

FIGURE 1.

Structure of the NiFe active site and mechanism of hydrogenase. The structure is based on Protein Data Bank code 1CC1 (50). The mechanism of hydrogenase activation and catalysis is based on the work of Lill and Siegbahn (28). The asterisks indicate an EPR-active state.

FIGURE 2.

Structure of F₄₃₀ at the MCR active site and mechanism of methane formation. The structure is derived from Protein Data Bank code 1HBN (46). The bound CoM was omitted from the structure to focus on the tetrapyrrole.