Transition Metals in Biochemistry

Transition metal ions in biological systems are of interest in biology, biochemistry, chemistry, medicine, and physics. Scien­ tists with rather different viewpoints, employing many methods, have contributed to this area. A concise review of the current state of the field will, to some extent, reflect the special knowledge of the person writing it - in this case application of physical methods to the investigation of metal coordination. x­ ray diffraction is one of the most important of these methods, but a useful treatment of X-ray structure analysis would be com­ parable in size with and beyond the scope of the monograph. Many results of X-ray diffraction studies are, of course, presented. Electron paramagnetic resonance spectroscopy has played a major part in the rapid advance in knowledge of the electronic struc­ tures of transition metal ions in biological systems. More gener­ ally, measurements involving light, microwaves, and magnetic fields are capable of producing much new information, and the required instrumentation is available at most research institu­ tions. Therefore light absorption and paramagnetic resonance are treated in depth. The principles described in the latter discus­ sions are broadly applicable, for example to the promising tech­ niques of X-ray spectroscopy (utilizing synchrotron radiation) and lanthanide-perturbed, very high-resolution nuclear magnetic resonance spectroscopy.

Contenu

1 The Role of Transition Metal Ions in Biological Oxidation and Related Processes.- 1. Transition Metal Ions.- 2. Prosthetic Groups.- 3. Equilibrium Considerations in Reactions of Transition Metals.- a) Site Stability: Equivalent Ligands, Chelation, and Other Factors.- b) Electron Transfer and Redox Potentials.- 4. Molecular Functions of Proteins Containing Transition Metal Ion Prosthetic Groups.- a) Oxygen Carriage.- b) Oxygen Utilization.- c) Hydroperoxide Reactions.- d) Electron Transfer, Protein to Protein.- e) Hydrogen Atom Transfer from Substrate to Coenzyme or Substrate.- f) Nitrogen Utilization.- g) Hydrogen Utilization.- h) Hydrogen Peroxide Formation from Superoxide Radicals.- i) Methyl Transfer and Internal Hydrogen Transfer.- j) Utilization, Production, and Transfer of Ammonia.- k) Oxygen Evolution.- 5. The Role Which a Transition Metal Ion Plays in the Function of a Protein.- 6. Experimental Methods.- a) Isolation and Identification of Prosthetic (Nonprotein) Ligands.- b) X-ray Diffraction from Protein Single Crystals.- c) Electron Paramagnetic Resonance and Related Measurements.- d) Optical Measurements.- e) Measurements Utilizing Nuclei.- 7. Some Aspects of the Role of the Polypeptide in the Functioning of Proteins Containing Transition Metal Ions.- 2 Metal Coordination in Proteins.- 1. Ligands.- 2. The Established Coordination in Several Proteins.- a) Insulin.- b) Carboxypeptidase.- c) Myoglobin and Hemoglobin.- d) Myohemerythrin and Hemerythrin.- e) Cytochrome c.- f) Cytochrome b5.- g) Copper, Zinc Superoxide Dismutase.- h) Rubredoxin.- i) Ferredoxin and High Potential Iron-Sulfur Protein (HiPiP).- 3. Covalency.- 4. Some Aspects of Differences in Heme Binding.- 3 Copper.- 1. Cupric Peptides.- 2. EPR of Cupric Peptides and Related Complexes.- 3. The Blue Proteins.- 4. Magnetic and Optical Properties of Quantum Mechanical Models of the Cupric Ion.- 5. "Nonblue" Coordination in Copper Proteins.- 4 Heme Iron.- 1. Valence and Spin States of Iron.- 2. Magnetic Susceptibility.- 3. Valence State Determination.- 4. Optical Properties.- 5. Spin State Equilibria.- 6. Influences of Symmetry upon the Energy Levels of Low- and High-Spin States.- 7. Ligand Hyperfine Effects in Ferric Hemeproteins.- 8. Iron Hyperfine Effects.- 9. Modified Hemes.- 10. Photodissociation and Recombination.- 5 Nonheme Iron and Molybdenum.- 1. Iron Storage and Transport Proteins.- 2. Iron-Sulfur Proteins.- 3. Molybdenum.- 6 Electronic Structures and Properties.- 1. Atomic Orbitals.- 2. Spin States.- 3. Transition Metal Ions.- 4. Ligands and Molecular Orbitals.- 5. Absorption of Light.- 6. Interaction of Transition-Metal Ions with an Applied Magnetic Field.- 7. Magnetic Interactions of the Metal Electrons with Nuclei in the Coordination Sphere.- 8. Optical Activity.- References.