Since its introduction, pulse radiolysis has been an important technique for examining the properties of organic and inorganic radicals, and for enumerating those reactions responsible for cellular damage by ionizing radiation. Biochemists, and biophysicists outside the area of radiation biology appear, perhaps for historical reasons, to have an incomplete appreciation of the technique's potential. Protein chemists in particular, have been only dimly aware of the numerous reports of, and the significant results obtained from pulse radiolysis studies of proteins. Our purpose here is to bring some of these results together in order to emphasize the power and usefulness of pulse radiolysis experiments both for elucidating enzyme reaction mechanisms, and for gaining information on the structure of proteins in aqueous solutions. Reviews containing related, or in part the same material to be covered here have appeared previously; for example, Land (1970), Adams et al. (1972a), Shafferman & Stein (1975), Adams & Wardman (1977). This review updates these earlier works, but more importantly approaches the topic of protein pulse radiolysis with a different emphasis.

Applications of pulse radiolysis to protein chemistry.

Purpose: To obtain a wider insight into the general properties of carnosine and to provide support to its anti-oxidative role. This property is hypothesized to be linked to various mechanisms including free-radical scavenging and metal chelation (i.e. Cu(II)). Methods: Pulse-radiolysis experiments were performed by a 12MeV electron linear accelerator (LINAC) on carnosine/ copper(II) (2:1) and carnosine aqueous solutions at different pH. Raman spectra of solid samples were obtained by a Bruker IFS 66 spectrometer. Results: As well as for free carnosine, in the presence of copper ions the interaction of carnosine with OH radicals involves the imidazole group of the molecule. The oxidation of copper (II)-carnosine system by OH radicals is related to the pH-dependent structure of the copper(II)-carnosine complex. Raman spectra indicate that at alkaline pH the formation of a dimeric species containing two carnosine molecules complexed to two Cu2+ ions takes place. This structure can address the OH attack more ...

Hydroxyl radical scavenging by carnosine and Cu(II)-carnosine complexes: a pulse-radiolysis and spectroscopic study.

The binding of copper(II) and zinc(II) to oxidized glutathione.

The reduction of Cu(II) complexes of histidine and histidyl peptides at mercury electrodes

investigated using the pulse radiolysis method. The hydrated electron, used as a reducing agent, was found to react with the complexes by a bimolecular process. In the Cu(II)histidine and Cu(II)-glycyl-histidine complexes at pH 11, the reaction with the eaq- is direct with the Cu (II) ion and no secondary reactions were found to occur up to 5 msec after the pulse. In the Cu(II)-glycyl-histidine complex at pH 6.5 and Cu(II)-3-alanylhistidine at pH 7.5, the decay of the electron was followed by the appearance of a transient absorption band centered at 360 nm. This band is assigned to the adduct of an electron in the imidazole ring of the histidyl peptides. The radical ion is formed by the direct reaction of the eaq- with the liganded histidyl residue. The Im- decays via a first order process at the same rate at which the Cu (II) ion is reduced. C02- reduces all the complexes studied via a bimolecular reaction. It is suggested that this is a direct reaction of the CO2- with the metal ion. An attempt to correlate these reaction steps

The reduction of Cu(II) complexes of histidine and histidyl peptides. A pulse radiolysis study.

The reduction mechanism of two Cu(II)--peptide complexes, Cu(II)-- (gly)$sub 3$ and Cu(II)--glutathione, was investigated using the pulse radiolysis method. The hydrated electron, used as a reducing agent, was found to react with the two complexes by a bimolecular process. In the Cu(II)--(gly)$sub 3$ complex the reaction of the e$sup -$/sub aq/is both with the Cu(II) ion and with the carbonyl group of the peptide bond to form a carbonyl ''electron adduct'' radical. This adduct transfers the electron in a first-order process to the Cu(II). In the Cu(II)--glutathione complex the decay of the electron was followed by an appearance of a transient absorption band centered at 410 nm. It was followed by a slower, small increase of absorption at the same wavelength (lambda/sub max/ = 410). This band is assigned to the adduct of an electron with the disulfide bond of the glutathione (RSSR$sup -$ radical ion). The radical ion is formed either by the direct reaction of e$sup -$/sub aq/ with the disulfide bond and the transfer of an electron from the carbonyl adduct formed by the e$sup -$/sub aq/ or entirely via the electron-transfer reaction from the adduct to the S-S bridge. The RSSR$sup -$ decays via a first-order process at the same rate at which the Cu(II) is reduced. CO$sub 2$$sup -$ reduces the Cu(II) ion in the complexes via a bimolecular reaction. In the Cu(II)--glutathione complex a small part (10 percent) of the reduction of the Cu(II) proceeds via the disulfide bridge. The pathway of the reduction of the Cu(II) ion in peptide complexes by the hydrated electron may therefore be delineated: It proceeds from the bimolecular encounter step, in which the electron is attached to residues of the peptide (carbonyl and disulfide groups), followed by an intramolecular process to the Cu(II) ion. (auth)

M. Faraggi

Papers

Pulse Radiolysis Studies of Electron-Transfer Reaction in Molecules of Biological Interest: II. The Reduction of Cu(II)-Peptide Complexes