Preparation and Characterization of Mercury and Silver Derivatives of an Engineered Purple Copper Center in Azurin

Abstract

Understanding the structure and function of purple copper centers in proteins have been the focus of recent studies.1,2 Purple copper centers, found in cytochrome c oxidase (COX)3 and nitrous oxide reductase,4 are a new class of copper centers in biology. They all display an intense purple color due to strong absorptions around 480, 530, and 800 nm,2 a typical EPR spectrum indicative of a mixed-valence binuclear copper center,5 and a characteristic resonance Raman Cu-S stretching frequency around 340 cm-1.6 Recent X-ray structural studies of two COX7 and one engineered cytochrome o quinol oxidase8 have shown that the purple copper center is a dithiolate-bridged binuclear copper center where both coppers are in distorted tetrahedral sites.