Prosthetic groups conformations

Figure 10.1 Conformation of epothilone D bound in the P450epol< active site. The figure was prepared from PDB entry 1PKF using Swiss-PdbViewer [27]. The heme prosthetic group is shown with its cysteinate ligand (Cys365) bound. For clarity, amino acids lining the active site have been omitted apart from Phe96.

The response current extremely decreased in the potential range above 0.6V probably due to an irreversible inactivation of FDH. The possible reasons for the inactivation at higher potentials might be (1) conformational change of FDH in such a manner as the enzyme loses its prosthetic group PQQ, and (2) a drastic change in pH of the molecular interface that causes the enzyme inactivated. 

It is quite evident that the ferrous complexes of porphyrins, both natural and synthetic, have extremely high affinities towards NO. A series of iron (II) porphyrin nitrosyls have been synthesized and their structural data [11, 27] revealed non-axial symmetry and the bent form of the Fe-N=0 moiety [112-116]. It has been found that the structure of the Fe-N-O unit in model porphyrin complexes is different from those observed in heme proteins [117]. The heme prosthetic group is chemically very similar, hence the conformational diversity was thought to arise from the steric and electronic interaction of NO with the protein residue. In order to resolve this issue femtosecond infrared polarization spectroscopy was used [118]. The results also provided evidence for the first time that a significant fraction (35%) of NO recombines with the heme-Fe(II) within the first 5 ps after the photolysis, making myoglobin an efficient N O scavenger. 

Fig. 15. Structure of the prosthetic group in (a) rhodopsin, where the retinal Schiff base is in an 1 l-co,6-j-cir-l2-s-ew conformation (b) delocalized excited singlet state (c) bathorhodopsin. where the chromophore is a hexaene amine-imidazole complex. From van der Meer et al. [127],...

The electronic properties of haemoproteins have been measured and discussed in recent years by workers whose primary interests cover a wide range of scientific disciplines, from theoretical physics to medicine and biology. In fact there can be few other fields in which so many disciplines have pooled their resources, both experimental and theoretical. In spite of the prodigious development of other physical methods electronic absorption spectroscopy remains the most widely-used tool in the study of these proteins. A proper understanding of their spectra is clearly of the greatest importance in the investigation of the molecular electronic structure of the haem chromophore, and of the effects of the structure and conformation of the polypeptide chain on the properties of the prosthetic groups derived from it. 

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