Spectroscope pocket

Introduction of tbiolate ligation at position 93 has also been reported (69, 70, 73). Again subtle species-specific differences in sequence on the proximal side of the heme binding pocket result in significant differences in behavior between closely related proteins. In this case, the spectroscopic properties of the human H93C variant (69, 70) were consistent with the presence of five-coordinate, cysteine-coordinated high-spin Fe(III). On the other hand, similar studies of the corresponding... 

It is clear that the g values are very sensitive to the presence or absence of hydrogen bonding to the quinone oxygens and to the hydrophobicity of the solvent surrounding or the protein pocket. Also the structure of the quinone itself plays a role.140 However, since the 0-tensor reflects only the global properties of the wavefunction it is still difficult to draw far reaching conclusions from this spectroscopic parameter. This situation will hopefully change when more reliable 0-tensor calculations, e.g. for radicals embedded in proteins, become available, e.g. on the QM/MM level. 

These conclusions are still consistent with the finding that significant conformational differences between Pr and Pfr do in fact exist ([65,147] for reviews see [8c, 148]). They can be rationalized—albeit not with conclusive rigour—by a conformational adaptation of the apoprotein part located around the bilatriene-binding pocket, following the Z E photoisomerization of the chromophore. This local change then should suffice to determine through bilatriene chromophore-protein interactions the spectroscopic characteristics of the chromophore as well as stability and reactivity of the two photochromic forms of phytochrome. 

Phosphaalkynes RC=P display a rich coordination chemistry, and five different modes of ligation (M-Q) may be discerned in phosphaalkyne transition-metal complexes (Scheme 25).3,51 According to theoretical calculations and to photoelectron spectroscopic investigations, the doubly degenerated jr-orbitals of the triple bond are the HOMOs in phosphaalkynes. In keeping with this, the rj2-coordination modes N-Q are usually realized with transition metals. Complexes with rjMigated phosphaalkynes M are only possible when the respective ensemble of metal atom and ancillary ligands form an appropriate pocket, which only allows rj1-coordination by a linear molecule.3,sl... 

The Qp site was found in a hydrophobic pocket near heme bl, formed by residues from aC, aF, and aef, below acdl, on the intermembrane space side of cytochrome b. No substrate structure in the Qp site has been reported. The site has been characterized using various inhibitors by a number of different research groups. The Qp site inhibitors are spectroscopically divided into two types class I, inhibitors which affect heme b (myxothiazol and MOA type inhibitors) class II, inhibitors which affect both heme bn and FeS cluster [stigmatellin, UBDBT [5-undecyl-6-hydroxy-4,7-dioxobenzothiazol).] We have succeeded in obtaining a class I inhibitor structure (myxothiazol) however, we were... 

The ligand binding pocket of USP is filled by a fortuitous phospholipid co-purified and co-crystallized with the USP LBD that was fiirther characterized by mass-spectroscopic and chemical analysis [57]. In a similar way, recent crystallographic investigations of the retinoid-acid related orphan receptor (3 (ROR (3) [58] and of the heterodimeric complex RARa/RXRa [30] revealed an E.coli endogeneous fatty acid in the ROR (3 and in the RXRa subunit, respectively. 

The heme environment of MPO, both in the proximal and distal heme pockets, is conserved in LPO. As with other peroxidases, LPO reacts with H2O2 to give compound I. In the absence of any electron-donor substrate, compound I decomposes to compound I species which is spectroscopically different from compound I. Compound II is formed spontaneously upon addition of one equivalent of... 

NO binds to the heme of sGC at a diffusion-controlled rate to form an initial 6-coordinate complex, which rapidly converts to a 5-coordinate ferrous nitrosyl complex (Fig. 3b) (52). The breaking of the Fe-His bond is thought to be critical to the activation of sGC by NO however, recent data has shown that the NO coordination to the heme is not sufficient for full activation (13, 56). A low-activity Fe -NO complex can be formed in the presence of stoichiometric amounts of NO, and this species is identical spectroscopically to the highly active form of the enzyme that is formed in the presence of substrate or excess NO. Based on these observations, two mechaiusms of NO activation have been proposed. One proposal is that excess NO activates the ferrous nitrosyl complex by binding to nonheme sites on the protein (13). The second proposal involves excess NO binding to the heme to form a transient dinitrosyl complex, which then converts to a 5-coordinate complex with NO bound in the proximal heme pocket (56). 

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