Peptide porphyrine-binding

The energetics of peptide-porphyrin interactions and peptide ligand-metal binding have also been observed in another self-assembly system constructed by Huffman et al. (125). Using monomeric helices binding to iron(III) coproporphyrin I, a fourfold symmetric tetracarboxylate porphyrin, these authors demonstrate a correlation between the hydropho-bicity of the peptide and the affinity for heme as well as the reduction potential of the encapsulated ferric ion, as shown in Fig. 12. These data clearly demonstrate that heme macrocycle-peptide hydrophobic interactions are important for both the stability of ferric heme proteins and the resultant electrochemistry. 

One of the first findings with respect to cytochrome c consisted of establishing the amino acid sequences immediately adjacent to the porphyrin ring and as a result identifying the mode of protein-porphyrin binding. When cytochrome c is digested with crystalline pepsin, a conjugated peptide is obtained. 

Calcium-binding proteins, 6, 564, 572, 596 intestinal, 6, 576 structure, 6, 573 Calcium carbonate calcium deposition as, 6, 597 Calcium complexes acetylacetone, 2, 372 amides, 2,164 amino acids, 3, 33 arsine oxides, 3, 9 biology, 6, 549 bipyridyl, 3, 13 crown ethers, 3, 39 dimethylphthalate, 3, 16 enzyme stabilization, 6, 549 hydrates, 3, 7 ionophores, 3, 66 malonic acid, 2, 444 peptides, 3, 33 phosphines, 3, 9 phthalocyanines, 2,863 porphyrins, 2, 820 proteins, 2, 770 pyridine oxide, 3,9 Schiff bases, 3, 29 urea, 3, 9... 

Bacterial pigments. Some bacteria commonly found in caries lesions are known to produce pigments. For example, the black staining of plaque is related with Actinomyces (Slots, 1974), but its chemical nature remains unknown. Black pigmented Prevotella produces both iron sulphide and heme pigments (Shah et ah, 1979). In addition, Propionibacterium forms porphyrins (Lee et al., 1978). Bacterial iron-binding peptides, which can contribute to discoloration, increase in the saliva of subjects with a high caries frequency (Nordh, 1969). 

Synthetic peptides containing side-chain modification have also been used as molecular scaffolds for the preparation of multiple receptors and molecular devices. 5 These include the use of crown ethers, cyclodextrins, porphyrins, and peptides with metal-binding sites (including ferrocenyl and EDTA side chains) (Section 9.4). Cyclization procedures have been developed to prepare biologically active cycloisodityrosine peptides which contain 14-or 17-membered rings (Section 9.5). The use of tryptathionine, a cross-linking dipeptide consisting of side-chain-to-side-chain linked L-Trp-L-Cys that is present in phallotoxins, 6 a family of cyclic heptapeptides, is also described (Section 9.6). 

Other templates have been described in the literature. Three independent groups used a porphyrin template. Sasaki and Kaiser utilized a porphyrin bearing four carboxylic acids (39) to prepare a synthetic metalloprotein with a four a-helix topology (40) [34], The utilization of a porphyrin template allows not only the templation of amphiphilic peptide segments, but also the incorporation of a metal binding site, which could serve eventually in a catalytic process (Fig. 16). 

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