Transition Metal Ions in Biology

5 Transition Metal Ions in Biology. Most high-field work in metallo- 

The same high-field advantage appeared in an investigation of the Mn binding site in cytochrome c oxidase from Paracoccus dentrificans. Spectra taken at W-band were considerably simplified compared with X-band and revealed contributions of a dipolar interaction between the Mn spin and the local CuA centre with a coupling constant of 33.6 G. This corresponded to an averaged distance of 9.4 0.2 A, which is consistent with the known X-ray structure of the material. 

A similar W-band study was performed on a new variant of lipoxygenase in which the iron is replaced by manganese (MnLO). Compared with X-band, the signal was considerably simplified at W-band and allowed estimates of the zero-field splitting parameter (D = 0.07-0.1 cm ) and E/D (0.13-0.23), which indicated that the coordination environment of MnLO is similar to that in iron lipoxygenase.  

In other systems, W-band EPR and X-band Fe-ENDOR have been used to characterize a new stable diiron centre found in the E. coli RNR mutant R2-Y122H. The spectrum was fully resolved at 94 GHz and evidence was given to support the view that the centre was a Fe Fe centre with a strongly coupled radical. Pulsed EPR at 95 GHz has been used to characterize the azurin mutant M121H, a blue copper protein, in a single-crystal study which allowed the complete g tensor to be determined relative to the molecular axes.  

A detailed structural study has also been made of oxygenated cobalt(II) heme model systems and oxygenated Co(II) corrin complexes. These used a combination of X-, Q- and W-band CW and pulsed EPR, X- and Q-band ENDOR, X-band HYSCORE and S-band ESEEM to determine the g and A tensors and investigate the proton and nitrogen hyperfine interactions. Both studies are excellent examples of the power of multi-frequency CW and pulsed ESR and ENDOR in determining the full electronic structure of metallo-complexes. 

---

A number of texts are now available on bioinorganic chemistry but ref. 26 provides a useful emphasis and account of the role of transition metal ions in biological systems. A number of texts - and reviews " on copper proteins are now available and individual chapters on the different functions of the copper proteins are contained in the various volumes of Metal Ions in Biological Systems edit by H. Sigel in particular, volumes 12 and 13 are almost exclusively devoted to c( per. In biological systems copper is the third most abundant transition metal element, with an occurrence of 80-120 mg in a normal human body (70 kg), compared to values of 4-5 g for iron and 1.4-2.3 g for zinc. It generally occurs in the copper(II) oxidation state, but is believed to involve a copper(I) oxidation state in deoxyhemocyanin (Section 53.3.5) and the copper(IIl) oxidation state has been invoked in mechanistic studies (Section 53.5). ... 

Interactions of histidine and other imidazole derivatives with transition metal ions in chemical and biological systems. R. J. Sundberg and R. B. Martin, Chem. Rev., 1974, 74, 471-517 (517). 

Tables 1.2-1.6 list some of the important geometries assumed by metal ions in biological systems. Common geometries adopted by transition metal ions that will...

Tables 1.2-1.6 list some of the important geometries assumed by metal ions in biological systems. Common geometries adopted by transition metal ions that will be of most concern to readers of this text are illustrated in Figure 1.3. It is important to remember that in biological systems these geometries are usually distorted in both bond length and bond angle.

Chapter 7 has reported on the importance of iron in biological species. Because iron is the most abundant transition metal found in biological species, one would expect a wide variety of iron-containing proteins and metalloenzymes. Only a few of these have been treated in any detail in this chapter. Little or no mention has been made of how or why iron ions evolved to be the most biologically abundant transition metal ions probably their usefulness in redox situations and for electron transport has something to do with their popularity. Iron homeostasis in biological species has not been discussed, although this... 

R.J. Sundherg u. R.B. Martin, Interaction of Histidine and Other Imidazole Dervatives with Transition Metal Ions in Chemical and Biological Systems, Chem. Rev. 74, 471 -517 (1974). 

M. T. Beck, Prebiotic Coordination Chemistry The Possible Role of Transition Metal Complexes in the Chemical Evolution , in Metal Ions in Biological Systems , ed. H. Sigel, Dekker, New York, 1978, vol. 7. 

Group 11 (or IB) contains copper, which is the third most common transition metal found in biological systems. Copper in solution has two stable oxidation states, cuprous (Cu1+) and cupric (Cu2+) ion. The ability of copper to easily accept and donate electrons explains its important role in oxidation-reduction reactions and... 

In this chapter, the unique features of transition metals in biological systems are discussed from the point of view of structural roles, spectroscopic properties, electron transfer, hydrolytic and redox catalysis, and metal-responsive gene expression. The following chapters provide more detail on these subjects. Several important examples not discussed elsewhere in this volume will be presented. The goal of this chapter (and this volume) is to acquaint the reader with the wide range of roles played by metal ions in biological systems and thereby to demonstrate why metals are such useful cofactors and why scientists from such broad disciplines are drawn to study their properties. 

Kozelka, J. "Molecular Modeling of Transition Metal Complexes with Nucleic Acids and Their Constituents." In Metal Ions in Biological Systems Sigel A., Sigel. H., (eds.) Marcel Dekker, Inc. New York, Basel, Hong Kong, 1996 Vol. 33 pp 2. 

---