EPR of Cobalt-Substituted Zinc Enzymes
Contribution to Book
Format of Original
Metals in Biology: Applications of High Resolution EPR to Metalloenzymes
Original Item ID
Co(II) is sometimes utilized as a spectroscopically active substitute for Zn(II) in enzymes. Metal binding sites in enzymes that contain catalytically active Zn(II) generally yield high-spin S = 3/2 Co(II) ions when substituted with cobalt, and these provide EPR spectra rich in information. Extracting this information involves an appreciation of the extent to which the properties of Co(II) mirror those of Zn(II), careful sample preparation and biochemical characterization, careful recording of the EPR data, and the ability to interpret spectra in a quantitative way. Here, the applicability of Co(II) as a structural and functional mimic of Zn(II) in enzymes is considered and a brief update of EPR studies in the literature is presented. Methods of substitution of Zn(II) by Co(II) are described. Recording EPR spectra of high-spin Co(II) that will provide useful information is not a trivial exercise, and experimental considerations are discussed in some detail. The analysis of EPR spectra in terms of spin-Hamiltonian parameters is described, along with their interpretation in structural terms. Complementary techniques to EPR are very briefly discussed, and a case study is presented as an example of how EPR of Co(II) can provide mechanistic information on a zinc enzyme that is unavailable by other techniques.