Metalloproteins characteristics

A terminal water or hydroxyl ligand is another source of proton hyperfine couplings in metalloproteins. Characteristically, these protons can usually be exchanged in deuterated media (unlike the constitutive protons discussed above), allowing for complementary H ENDOR studies on the exchanged samples. For example, ENDOR resonances from exchangeable... 

Sumi H (1998) V-I characteristics of STM processes as a probe detecting vibronic interactions at a redox state in large molecular adsorbates such as metalloproteins. J Phys Chem B 102 1833-1844... 

Electronic spectra of metalloproteins find their origins in (i) internal ligand absorption bands, such as n->n electronic transitions in porphyrins (ii) transitions associated entirely with metal orbitals (d-d transitions) (iii) charge-transfer bands between the ligand and the metal, such as the S ->Fe(II) and S ->Cu(II) charge-transfer bands seen in the optical spectra of Fe-S proteins and blue copper proteins, respectively. Figure 6.3a presents the characteristic spectrum of cytochrome c, one of the electron-transport haemoproteins of the mitochondrial... 

The goal of many biomolecular NMR studies is characterization of global molecular structure. In metallo-biomolecules, and in particular, for paramagnetic species, it is sometimes preferable to use NMR to perform a more focused study of the metal ion coordination enviroiunent and the metal electronic structure. Metal sites show great variation in the effects on chemical shifts and line widths and thus often call for tailored approaches. In this section, characteristics of some of the metalloproteins metal sites most frequently studied by NMR are summarized. Examples have been selected to illustrate approaches described in this chapter such as metal substitution, use of pseudocontact shifts, RDCs, relaxation enhancement, and detection of nuclei other than H. 

ICP-MS was found to be compatible with LC for the trace metal speciation. The role of ICP-MS in trace element speciation studies at the FSL was described (Crews et al., 1987). The characteristics of LC-ICP-MS for the study of metalloprotein species were assessed and the chromatographic efficiency of ICP-MS was found to be similar to that obtained with a UV detector (Dean et al., 1987). Information about the chemical nature of trace elements from food can be obtained by first treating the foods in vitro with enzymes to broadly simulate the action of enzymes in the gastrointestinal tract (Crews et al., 1988). The soluble components can be separated by size exclusion chromatography (SEC) and an estimate of their molecular size obtained. By coupling SEC... 

NOS products of neurons, epithelial cells and other cells in the lung have both bronchodilator and inflammatory properties (Gaston etal., 1994b) the specific nature of this bioactivity depends on the chemical characteristics of the functional products in the specific microenvironment under consideration. For example, NO is capable of complexing with and affecting the activity of a variety of metalloproteins and enzymes, such as guanylyl cyclase and ribonucleotide reductase (Nathan, 1992 Stamler et al., 1992). NO can also complex with superoxide anion to form peroxynitrite, which has a cytotoxic immune effector role (Radi etal., 1991 Stamler etal., 1992). Furthermore, NO can form iron nitrosyl complexes, which are the putative intracellular macrophage products of iNOS responsible for lysis of intracellular parasites (Hibbs... 

The study of metals in biological systems requires techniques, some of them highly specific, some limited to specific characteristics of the metal ion in question, some of more general applicability. Thus, Mossbauer spectroscopy in biological systems is restricted to iron-containing systems because the only element with a Mossbauer nucleus available is Fe. The EPR spectroscopic techniques will only be of application if the metal centre has an unpaired electron. In contrast, provided that suitable crystals can be obtained. X-ray diffraction allows the determination of the three-dimensional structure of metalloproteins and their metal centres. 

While many proteins in tissues may thus easily form copper complexes, there are a few proteins of which copper is an integral part. Copper in these proteins is part of the molecular structure and not in dissociation equilibrium with ionic copper in the solution there is a characteristic ratio between moles of protein and atoms of associated copper. These and a few other criteria, discussed in detail by Vallee (V3), make these proteins a special class of metal-protein complexes and establish them as metalloproteins. 

An ever increasing number of copper metalloproteins is being recognized. Those regularly present in mammals are listed in Table 5 with some of their characteristics. Other important naturally occurring copper proteins, such as hemocyanin, laccase, and ascorbic acid oxidase, are not listed since they do not occur in mammals. The metalloprotein nature of some of the proteins listed in Table 5 has not been established fully as yet. The search for further copper proteins, copper-protein complexes, and other forms in which copper may be stored or transported in the body must continue. 

The EPR data supported the electrophoretic, spectroscopic, and enzymic proofs of a successfully reconstituted erythrocuprein. It was surprising that the aerobically reconstituted erythrocuprein and even the 4 Cu2+ apoprotein showed most of the EPR characteristics of the 2 Cu—2 Zn enzyme. Only the A n values of the 4 Cu protein and the aerobically reconstituted erythrocuprein were different. It is suggested that in the last two metalloproteins the Cu2+ ligand distances are somewhat distorted or the ligands are slightly displaced due to conformational changes in the protein portion (Talbe 8). 

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