PBP complexes

As far as electron absorption spectra of the Co(II) PBP complex are concerned, they have still been insufficiently explained (1,56,67,86). Gerloch et al. (86) discussed the spectra of the [Co(H2dapsc) (C1)(H20)]+ and [Co(H2dapsc)(H20)2]2+ cations in some detail and the bands at 632, 562, 549(sh), and 507(sh) nm of the former, and those at 628, 540, and 526(sh) nm of the latter complex, were ascribed to transitions between components of the 4P term. These authors found that all spin-allowed d-d transitions occur at energies below 500 nm,... 

Only three PBP complexes of Fe(III) with acyclic ligands from the class of bis(acylhydrazone) of dap have been structurally characterized at present (41,49,53) and this prompted studies in that direction. Both direct and template synthesis afforded the complex [Fe(Hdapsox) Cl2] - 1/2H20 (9) with a monoanionic H2dapsox ligand (7). Protonation of the coordinated ligand was unsuccessful even upon addition of HC1 to the reaction mixture (Scheme 5). In spite of asymmetrical mono-deprotonation, the ligand was symmetrically pentadentately... 

Since these intermediates were characterized (10) as monomeric PBP complexes of Fe(III) with a dianionic acyclic pentadentate ligand, it was the intention to isolate and structurally characterize some of them, since no examples of such structures have been reported in the literature. With this aim, the [Fe(dapsox)(H20)2]C104 complex 12 was synthesized, which is analogous to the intermediate [Fe(dapsox)Cl(H20)]. The results of an X-ray structural analysis (Fig. 6) confirmed the PBP structure of the complex and double deprotonation of the ligand. This structure is the first example of a monomeric structure of Fe(III) with an anionic pentadentate ligand and confirms previously suggested hydrolytic processes (10) which led to the production of complex 10. 

Mechanism of pheromone binding and release 15.3.1 The pheromone-PBP complex... 

Is and PBPRP1 may then represent an OBP-1 type of protein defined by key residues that may underlie specific functions. The ABPX/PBPRP-specific amino acid residues arginine at position 16, lysine at position 47, proline at position 76, threonine at position 92 are replaced respectively by leucine, glycine, lysine and lysine residues that are conserved in the different types of binding protein from B. mori (Krieger et al., 1993 Picimbon, 2001). These replacements may be relevant to support the function of ABPX. Based on the crystal structure of the bombykol-PBP complex, the tryptophane at position 101 and the valine 105 have been shown to contact the molecule of Bombykol (Sandler et al., 2000). These are replaced by two threonine residues characteristic of OBP-1. Therefore, the threonine residues characteristic of OBP Is may be of crucial importance for the binding specificities of these proteins. 

Consider PBP complexes witb a d" electronic configuration in which there is one carbonyl ligand, in either an axial (Li) or an equatorial position (choose the position L2). 

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