[6 Redox Control of Zinc Finger Proteins

By Michael A. Baldwin and Christopher C. Benz

Introduction

Recognized as an essential trace element for well over a century, zinc is the second most abundant metal ion in mammalian cells, with the adult human body containing up to 3 g of ionic zinc (Zn24).1 Unlike transition metal cations such as chromium, nickel, iron, and copper, which can engage in Fenton/Haber-Weiss chemistry intracellularly to generate free radicals and induce potentially carcinogenic oxidative damage,2 Zn2+ produces structure-stabilizing protein cross-links without the undesirable effects of metal ion redox reactivity. Since 1940, it has been known that Zn2+ is structurally essential for the catalytic activity of critical enzymes (e.g., carbonic anhydrase, alkaline phosphatase, lactate dehydrogenase, superoxide dismutase, and RNA and DNA polymerases), in which it is often tetravalently coordinated by imidazole nitrogens (from histidines) and carboxylic groups (e.g., glutamic or aspartic acid). In most of these enzymes, zinc catalyti-cally interacts with the substrate molecule undergoing transformation; in some it

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