Cupric Cation Effects on Conformation of Silk Fibroin

Hōjō, Nobumasa; Shirai, Hirofusa; Takayama, Kimiko; Owa, Kimiko

doi:10.1246/nikkashi1898.72.2_470

Cited by 2 publications

(2 citation statements)

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“…pH-Dependent Cu(II) Coordination Modes and Sites in Cu(II)−SF Complexes. Cu(II) has been shown to have a strong affinity and can form stable complexes with biological molecules, such as copper proteins (), prion proteins ( − ), amyloid β-peptides ( , ), sericin (), and silk fibroin ( − ). In general, the most likely ligands coordinating with Cu(II) are histidine, tyrosine, serine, tryptophan residues, etc.…”

Section: Discussionmentioning

confidence: 99%

“…However, the maximum silk II content is achieved at a Cu(II) content of 0.63 mg of Cu/g of SF for pH 6.9 or 8.0 as compared to a Cu(II) concentration of 0.36 mg of Cu/g of SF at a pH of 5.2. (51), prion proteins (25)(26)(27)(28)(29), amyloid β-peptides (30,31), sericin (52), and silk fibroin (53)(54)(55). In general, the most likely ligands coordinating with Cu(II) are histidine, tyrosine, serine, tryptophan residues, etc.…”

Section: Ph-dependent Cu(ii) Coordinationmentioning

confidence: 99%

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Effect of pH and Copper(II) on the Conformation Transitions of Silk Fibroin Based on EPR, NMR, and Raman Spectroscopy

et al. 2004

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Much attention has been paid to the natural mechanism of silkworm spinning due to the impressive mechanical properties of the natural fibers. Our results in the present work show that the fractional changes of the conformational components in regenerated silk fibroin (SF) extracted from Bombyx mori fibers is remarkably pH- and Cu(II)-dependent as demonstrated by Cu(II) EPR, (13)C NMR, and Raman spectroscopy. Cu(II) coordination atoms in SF are changed from four nitrogens to two nitrogens and two oxygens as well as to one nitrogen and three oxygens when the pH is lowered from 8.0 to 4.0. The addition of a given amount of Cu(II) into a SF solution could induce efficiently the SF conformational fractional change from silk I, a soluble helical conformation, to silk II, an insoluble beta-sheet conformation. This behavior is strikingly similar to that seen in prion protein and amyloid beta-peptide. On the basis of the similarity in the relevant sequence in SF to the octapeptide PHGGGWGQ in PrP, we suggest that at basic and neutral pH polypeptide AHGGYSGY in SF may form a 1:1 complex with Cu(II) by coordination of imidazole N(pi) of His together with two deprotonated main-chain nitrogens from two glycine residues and one nitrogen or oxygen from serine. Such a type of coordination may make the interaction between two adjacent beta-form polypeptide chains more difficult, thereby leading to an amorphous structure. Under weakly acidic conditions, however, Cu(II)-amide linkages may be broken and Cu(II) may switch to bind two N(tau) from two histidines in adjacent peptide chains, forming an intermolecular His(N(tau))-Cu(II)-His(N(tau)) bridge. This type of coordination may induce beta-sheet formation and aggregation, leading to a crystalline structure.

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Section: Discussionmentioning

confidence: 99%

Section: Ph-dependent Cu(ii) Coordinationmentioning

confidence: 99%

Effect of pH and Copper(II) on the Conformation Transitions of Silk Fibroin Based on EPR, NMR, and Raman Spectroscopy

et al. 2004

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Catalytic activity of Cu(II)–poly(vinyl alcohol) complex for decomposition of hydrogen peroxide

Hōjō

Shirai

Chujo

et al. 1978

J. Polym. Sci. Polym. Chem. Ed.

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Decomposition of hydrogen peroxide was examined was examined by using Cu(II)–poly(vinyl alcohol) (PVA) as catalyst. The rates of decomposition were measured. Electronic spectra and infrared spectra of Cu(II)–PVA complex systems were determined at various stages of decomposition. Effect of addition of various amines to the Cu(II)–PVA system on catalytic action was considered. The relation between the initial rate and the initial concentration of hydrogen peroxide varied in accordance with the rate expression of Michaelis‐Menten type. Cu(II)–PVA complex was found to have a large catalytic activity, while the polymeric PVA ligand and copper(II) ion exhibited less activity than Cu(II)–PVA complex. For hydrogen peroxide decomposition, Cu(II)–PVA complex showed catalytic activity when a stable complex of planar structure formed, while many other polymer complexes reported by other authors showed the catalytic activity when they were in unstable complex forms. An amine substituent has a critical influence on the rate of hydrogen peroxide decomposition. The mechanism in the first step of reaction for hydrogen peroxide decomposition is discussed.

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Cupric Cation Effects on Conformation of Silk Fibroin

Cited by 2 publications

References 0 publications

Effect of pH and Copper(II) on the Conformation Transitions of Silk Fibroin Based on EPR, NMR, and Raman Spectroscopy

Effect of pH and Copper(II) on the Conformation Transitions of Silk Fibroin Based on EPR, NMR, and Raman Spectroscopy

Catalytic activity of Cu(II)–poly(vinyl alcohol) complex for decomposition of hydrogen peroxide

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