Metalloproteins environment

Table 9 gives some cases where the rotational strengths of absorption bands have been measured in metalloproteins. At the present time these changes are not used to diagnose the nature of the ligands of the metal but rather they have been used to follow minor changes at the metal when substrates or inhibitors interact with the metals. The sensitivity of CD and MCD measurements to very small changes in the metal environment make them very attractive for protein/metal complex studies. 

Volume 226. Metallobiochemistry (Part C Spectroscopic and Physical Methods for Probing Metal Ion Environments in Metalloenzymes and Metalloproteins) Edited by James F. Riordan and Bert L. Vallee... 

Zinc is the active metal in the largest group of metalloproteins found in the nature. Recently a new class of zinc enzymes with a sulfur-rich environment has emerged the thiolate-alkylating enzimes, the most prominent of which is the cobalamine-independent methionine synthase.126 For these reasons several monothiolate zinc complexes have been prepared for the modelling of these enzymes with different N2S as (13),127 130 N20,13° 132 N3,132,133 S3,134 tripod ligands, or with Cd because of the favourable spectroscopic properties with an S3 tripod ligand.135... 

In the case of metalloproteins, at least two additional categories of mutation may be considered mutations that affect the coordination environment of the metal center and mutations that affect the ligand binding and/or electron transfer properties of the protein without modification of the coordination... 

Before plunging into a discussion of how such complexes are prepared, it is perhaps worthwhile to consider explicitly the rationale for such activity. The synthesis and characterization of accurate model complexes for a given metal site in a protein or other macromolecule allows one to (l) determine the intrinsic properties of the metal site in the absence of perturbations provided by the protein environment or (il) in favorable cases, deduce the structure of the metal site by comparison of corresponding physical and spectroscopic properties of the model and metalloprotein (3). The first class of model complexes has been termed "corroborative models" by Hill (4), while the second are termed "speculative models" (4). To date, virtually all the major achievements of the synthetic model approach have been in development of corroborative models. 

Probing Metalloproteins Electronic absorption spectroscopy of copper proteins, 226, 1 electronic absorption spectroscopy of nonheme iron proteins, 226, 33 cobalt as probe and label of proteins, 226, 52 biochemical and spectroscopic probes of mercury(ii) coordination environments in proteins, 226, 71 low-temperature optical spectroscopy metalloprotein structure and dynamics, 226, 97 nanosecond transient absorption spectroscopy, 226, 119 nanosecond time-resolved absorption and polarization dichroism spectroscopies, 226, 147 real-time spectroscopic techniques for probing conformational dynamics of heme proteins, 226, 177 variable-temperature magnetic circular dichroism, 226, 199 linear dichroism, 226, 232 infrared spectroscopy, 226, 259 Fourier transform infrared spectroscopy, 226, 289 infrared circular dichroism, 226, 306 Raman and resonance Raman spectroscopy, 226, 319 protein structure from ultraviolet resonance Raman spectroscopy, 226, 374 single-crystal micro-Raman spectroscopy, 226, 397 nanosecond time-resolved resonance Raman spectroscopy, 226, 409 techniques for obtaining resonance Raman spectra of metalloproteins, 226, 431 Raman optical activity, 226, 470 surface-enhanced resonance Raman scattering, 226, 482 luminescence... 

Gray, H. B. Electronic absorption spectroscopy. In Methods for Determining Metal Ion Environments in Proteins Structure and Function of Metalloproteins (Damall, D. W., Wilkins, R. G., eds.), New York-Amsterdam-Oxford, Elsevier/North-Holland, 1980, pp. 14-22... 

The mechanism of the regulation of electron transfer in metalloproteins has been investigated 61) and two relevant examples have been discussed in the first one the molecular mechanism controlling the electron transfer reactions is restricted to the immediate chemical environment of the metal center (azurin), while in the second one it involves a conformational transition of the whole quaternary structure of the enzyme. The power of the kinetic approach in detecting significant intermediates was emphasized 6t>. The Cu metal complex site of azurin has a distorted tetrahedral... 

Figure 10-5. The environment of the metal in a series of zinc metalloproteins. The proteins are (a) human carbonic anhydrase II, (b) thermolysin from Bacillus thermoproteolyticus, and (c) bovine pancreas carboxypeptidase. Each of these enzymes is, essentially, hydrolytic.

However, the changes in environment which occurred with the change from a reductive to an oxidative atmosphere rendered iron sulfide-based redox systems inconvenient, as they were very sensitive to (irreversible) oxidation. We saw in earlier chapters the facile formation of porphyrin and phthalocyanines from relatively simple precursors, and these systems were adopted for the final steps of electron transfer in oxidative conditions. The occurrence of iron centres in planar tetradentate macrocycles is ubiquitous, and metalloproteins containing such features are involved in almost every aspect of electron transfer and dioxygen metabolism. A typical example is seen in the electron transfer protein cytochrome c (Fig. 10-10). 

Research on metalloproteins, particularly enzymes and changes in the environment of free radicals introduced into biological structures (e.g., membranes). 

Study of the metal coordination environment in metalloproteins, nucleic acids, carbohydrates, membranes... 

---