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Role of Na⁺ and K⁺ in Enzyme Function

Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri

Metal complexation is a key mediator or modifier of enzyme structure and function. In addition to divalent and polyvalent metals, group IA metals Na⁺ and K⁺ play important and specific roles that assist function of biological macromolecules. We examine the diversity of monovalent cation (M⁺)-activated enzymes by first comparing coordination in small molecules followed by a discussion of theoretical and practical aspects. Select examples of enzymes that utilize M⁺ as a cofactor (type I) or allosteric effector (type II) illustrate the structural basis of activation by Na⁺ and K⁺, along with unexpected connections with ion transporters. Kinetic expressions are derived for the analysis of type I and type II activation. In conclusion, we address evolutionary implications of Na⁺ binding in the trypsin-like proteases of vertebrate blood coagulation. From this analysis, M⁺ complexation has the potential to be an efficient regulator of enzyme catalysis and stability and offers novel strategies for protein engineering to improve enzyme function.

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