Protein charge transfer interactions

C20-0102. Blue copper proteins are blue when they contain Cu but colorless as Cu compounds. The color comes from an interaction in which a photon causes an electron to transfer from a sulfur lone pair on a cysteine iigand to the copper center. Why does this charge transfer interaction occur for Cu but not Cu+ ... 

In this chapter results of the picosecond laser photolysis and transient spectral studies on the photoinduced electron transfer between tryptophan or tyrosine and flavins and the relaxation of the produced ion pair state in some flavoproteins are discussed. Moreover, the dynamics of quenching of tryptophan fluorescence in proteins is discussed on the basis of the equations derived by the present authors talcing into account the internal rotation of excited tryptophan which is undergoing the charge transfer interaction with a nearby quencher or energy transfer to an acceptor in proteins. The results of such studies could also help to understand primary processes of the biological photosynthetic reactions and photoreceptors, since both the photoinduced electron transfer and energy transfer phenomena between chromophores of proteins play essential roles in these systems. 

M cm ) at 500 and 600 nm were found to be common characteristics. This light absorption is due to charge-transfer interactions between iron and its ligands, particularly the /x-oxo bridge. In the active form of protein R2, the tyrosyl radical contributes to the light absorption with a sharp band at about 410 nm (e = 6600 M cm ) and a broader feature around 390 nm (e = 2000 M cm ) in the E. coli protein (77). In mouse R2 the sharp band is at about 415 nm (79). 

Elevated pressures can induce functional and structural alterations of proteins. The effects of pressure are governed by Le Chatelier s principle. According to this principle, an increase in pressure favours processes which reduce the overall volume of the system, and conversely increases in pressure inhibit processes which increase the volume. The effects of pressure on proteins depend on the relative contribution of the intramolecular forces which determine their stability and functions. Ionic interactions and hydrophobic interactions are disrupted by pressure. On the other hand, stacking interactions between aromatic rings and charge-transfer interactions are reinforced by pressure. Hydrogen bonds are almost insensitive to pressure. Thus, pressure acts on the secondary, tertiary, and quaternary structure of proteins. The extent and the reversibility, or irreversibility, of pressure effects depend on the pressure range, the rate of compression, and the duration of exposure to increased pressures. These effects are also influenced by other environmental parameters, such as the temperature, the pH, the solvent, and the composition of the medium. 

Multiple regression analysis based on Eq. 2 revealed that the cytotoxic activity mainly depended on the log P and a low Elumo value. It has been suggested that receptor protein tryptophan residues containing an aromatic ring moiety should be the best electron donor for charge transfer interactions with phenols because of their high Ehomo value [67]-... 

Fluorescence spectroscopy is a sensitive tool for investigating interactions between proteins and small molecules. Fluorescence changes can be observed as a result of conformational changes. In addition, charge transfer interaction with tryptophan residues influences the fluorescence properties. 

The SERRS excitation profile of protein-bound FAD is expected to follow closely the absorption spectrum of GO in solution, in accordance with SERRS investigations of dyes . Significant differences in the excitation profile are an indication of charge transfer interactions between the adsorbate and Ag. Again, this would require direct contact of the FAD with the Ag surface. 

Charge transfer interactions are also thought to be important in the interaction between drugs and proteins. These interactions are quite weak being <1 eV. A commonplace example is the complex formed between picric acid and creatinine (Fig. 1.10) in solution which is used as a... 

Such interactions are also possible between ions and dectron-rich systems. In some cases, charge transfer interactions may be involved in receptor binding, e.g. interactions between a quaternary ammonium centre in a dmg and phenylalanine side chains in a protein (Fig. 1.11). 

Slifkin, M. A. in Charge Transfer Interactions of Biomolecules (M. A. Slifkin, Ed.), Chapter 3, Amino Acids and Proteins, p. 52-75. London-New York Academic Press. 1971. 

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