Metalloenzymes

The term "metalloenzyme" refers to a large class of enzymes that use a metal cation as a cofactor in the active site. A wide variety of reactions, including hydrolytic processes and oxidation/reductions, are promoted by the enzymes. Examples include vitamin B-dependent enzymes that transfer methyl groups between molecules, nitrogenases that fix nitrogen from the atmosphere, proteases that cleave amide bonds, phosphodiesterases that cleave phosphate ester bonds, superoxide dismutases that destroy superoxide anion, hydrogenases that encourage the uptake of molecular hydrogen, and ribozymes that go through self-cleaving reactions. 5–9 The metal cation plays a unique role in each of the aforementioned systems by acting as a Lewis acid or a redox partner and enhancing substrate binding, which increases the ground state energy of the reaction partners and facilitates the catalysed reaction.