Heme coordination environment

The H64 distal ligand of wild-type myoglobin does not coordinate to the heme iron in either the reduced or the oxidized form of the native protein but stabilizes the coordination of a distally boimd water molecule of metMb. Replacement of H64 with other amino acid residues can, therefore, change the coordination environment of the heme iron in two ways. Such variants either may possess a distal residue that is able to coordinate to the heme iron or may possess a distal residue that is incapable of either coordinating to the iron or of forming a hydrogen bond with a coordinated water molecule. 

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... 

Similarly, this amphiphilic polymer micelle was also used to dismpt the complex between cytochrome c (Cc) and cytochrome c peroxidase (CcP Sandanaraj, Bayraktar et al. 2007). In this case, we found that the polymer modulates the redox properties of the protein upon binding. The polymer binding exposes the heme cofactor of the protein, which is buried in the protein and alters the coordination environment of the metal. The exposure of heme was confirmed by UV-vis, CD spectroscopy, fluorescence spectroscopy, and electrochemical kinetic smdies. The rate constant of electron transfer (fc°) increased by 3 orders of magnimde for the protein-polymer complex compared to protein alone. To establish that the polymer micelle is capable of disrupting the Cc-CcP complex, the polymer micelle was added to the preformed Cc-CcP complex. The observed for this complex was the same as that of the Cc-polymer complex, which confirms that the polymer micelle is indeed capable of disrupting the Cc-CcP complex. 

The pH dependence of cytochrome c oxidation-reduction reactions and the studies of modified cytochrome c thus demonstrate that the coordination environment of the iron and the conformation of the protein are relatively labile and strongly influence the reactivity of the metallo-protein toward oxidation and reduction. The effects seen may originate chiefly from alterations in the thermodynamic barriers to electron transfer, but the conformation changes are expected to affect the intrinsic barriers also. One such conformation change is the opening of the heme crevice referred to above. The anation and Cr(II) reduction studies provide an estimate of 60 sec 1 for this process in Hh(III) at 25°C (59). To date, no evidence has been found for a rapid heme-crevice opening step in ferrocytochrome c. 

It is now widely agreed that both copper and iron are essential components 52-56). The metal content (11 nmoles/mg protein) and the iron to copper ratio (1.0) are well established for the bovine enzyme, whereas in yeast the reported metal contents are higher and more variable (5-15 nmoles of iron per milligram of protein) and the copper to iron ratio is greater than unity ( 1.5) (Table II) (44-4 > 48-52, 57-59). The iron is present as the unusual heme, heme A, with an apparently unique structure (Fig. 2) 60). The coordination environment of copper is far less clear, but the easy reducibility of copper seems to require a ligand envi-... 

Influence of the active site environment on heme coordination and reactivity... 

The biological catalytic activity of metalloproteins for redox reactions is usually associated with a particular coordination environment of the metal active site [160, 161], In particular, there has been considerable interest in 02-binding and -activation by non-heme metalloenzymes [162-167). A redox-active metal center is often associated with another metal center which can accelerate the redox process of O2... 

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