Globular heme

Porphyrin-based self-assembled molecular squares 389 can form mesoporous thin films in which the edge of a square, thus the size of the cavity, can be adjusted by appropriate choice of substituents [8]. Fibers that form coil-coiled aggregates with distinct, tunable helicity are built from crown ethers bearing porphyrins 390 [9]. In addition to the porphyrin applications discussed in Sections 6.3.2.2 and 6.4, dendrimer metalloporphyrins 391 to be applied in catalysis [10] and the water-soluble dendritic iron porphyrin 319 modelling globular heme proteins [11] can be mentioned. 

Dandliker, P. J., Diederich, F., Gisselbrecht, J. P., Louati, A., Gross, M., Water-soluble dendritic iron porphyrins Synthetic models of globular heme proteins. Angew. Chem., Int. Ed. Engl. 1996, 34, 2725-2728. 

Dandliker PJ, Diederich F, Gisselbrecht J-P, Louati A, Gross M (1996) Water-soluble dendritic iron porphyrins synthetic models of globular heme proteins. Angew Chem Int Ed 34(23-24) 2725-2728... 

Privalov et al (1989) studied the unfolded forms of several globular proteins [ribonuclease A, hen egg white lysozyme, apomyoglobin (apoMb), cytochrome c, and staphylococcal nuclease]. Unfolding was induced by 6 M Gdm-HCl at 10°C, heating to 80°C, or by low pH at 10°C with cross-links cleaved (reduction and carboxamidomethylation or removal of heme). The unfolded forms showed CD spectra (Fig. 27)... 

The first three-dimensional structure of a protein determined was the dioxygen transporter myoglobin isolated from sperm whale in the ferric form (86, 87). A 153 amino acid globular protein, myoglobin contains eight helical regions (A to H) with a single heme b bound between helices... 

Myoglobin was the first protein to have its three-dimensional structure solved by X-ray crystallography. It is a globular protein made up of a single polypeptide chain of 153 amino acid residues that is folded into eight a-helices. The heme prosthetic group is located within a hydrophobic cleft of the folded polypeptide chain. 

The structure of cytochrome c determined by Dickerson and his colleagues (23, 24, 25, 26) is depicted in Figure 1. The heme group, which lies in a crevice of the essentially globular protein, is covalently bonded to the protein by thioether bridges between the porphyrin ring and two cysteine residues in the peptide chain. The iron atom is situated... 

According to the experimental data on rate constants of spin exchange at encounters between heme groups and nitroxides presented in Table 4.2., the accessibility of the heme group of cytochrome c to the encounters with neutral spin-probes IV is -31-33 times lower than that observed for free hemin. At present, it is difficult to separate the effect of heme group immersion into the protein globular structure from that of association in the relatively concentrated solutions (2-10mM) utilized in these studies. 

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