ISSN:0021-2148    

DOI:10.1002/ijch.197200108

出版商:WILEY‐VCH Verlag    

年代:1972

数据来源: WILEY

摘要:

AbstractThe different ways to generate the hydroperoxy radical are described. Both chemical and physical properties of the radical are summarized. The features of complexes of HO2with various cations, their fast exchange and their possible role in biological systems is discussed.

ISSN:0021-2148    

DOI:10.1002/ijch.197200109

出版商:WILEY‐VCH Verlag    

年代:1972

数据来源: WILEY

摘要:

AbstractThe main types of biochemically important electron transfer substances can be made to undergo reactions under irradiation which in some ways mimic those which occur in nature. In the case of NAD+, pulse radiolysis shows that electrons add to the pyridine ring forming an NAD· radical with a characteristic absorption in the visible range which is capable of transferring its electron to oxygen. Using simpler pyridinyl compounds it has been found that, as well as the absorptions in the visible range, the radicals exhibit absorptions in the infrared range which correlate well with transitions which may be deduced from the known charge‐transfer bands of the parent compound. The NAD· radical can be made by one‐electron oxidation of NADH as well as by reduction of NAD+, and the reaction with oxygen enables NADH to be converted into NAD+by an unambiguous free radical route. Cytochrome‐ccan be reduced either by hydrated electrons or CO2−. In solution buffered to neutral pH, the reduction gives rise immediately to normal reduced cytochrome‐c, but in mildly alkaline solution, an unstable reduced form appears whose conformation changes over a fraction of a second to that of normal reduced cytochrome‐c. As well as the hydrated electron and CO2−, the superoxide anion radical O2−has also been found to reduce cytochrome‐c. This reaction is very slo

ISSN:0021-2148    

DOI:10.1002/ijch.197200110

出版商:WILEY‐VCH Verlag    

年代:1972

数据来源: WILEY

摘要:

AbstractThe formation of ferrocytochromecupon pulse radiolysis of aqueous solutions of ferricytochromechas been studied by following spectral shifts at 550 nm and 700 nm. The reaction between ferricytochromecand hydrated electrons was studied by following the decay of hydrated electrons as well as the ferrocytochromecformation. The two processes proceed with the same rate which indicate diffusion‐controlled processes with a second order rate constant of 1.1 × 1011M−1sec−1. The reaction between ferricytochromecand H atoms was studied in a system containing H atoms only and found to be a second order reaction with a rate constant of 1.5 × 1010M−1sec−1. The formation of ferrocytochromecby reaction between ferricytochromecand OH radicals proceed by a first step with a second order rate constant of 1.4 × 1010M−1sec−1during which OH radicals react with the protein part of ferricytochromecforming an organic radical. Some of these radicals then undergo intramolecular reduction with a rate constant o

ISSN:0021-2148    

DOI:10.1002/ijch.197200111

出版商:WILEY‐VCH Verlag    

年代:1972

数据来源: WILEY

摘要:

AbstractThe applicability of the pulse radiolysis technique for understanding the election transfer mechanism in redox proteins is presented. It is also suggested that the observed redox reactivity of the protein is correlated to its structural features.

ISSN:0021-2148    

DOI:10.1002/ijch.197200112

出版商:WILEY‐VCH Verlag    

年代:1972

数据来源: WILEY

摘要:

AbstractThe reactions of H atoms, OH radicals and hydrated electrons acting as isolated reagents upon ribonuclease in dilute aqueous solution were studied by the technique of pulse radiolysis‐kinetic spectroscopy. The experiments show that initial action of these reagents upon the protein molecule is followed by intramolecular transformations. Two consecutive intramolecular steps have been observed in the reaction of H atoms, with specific rates of approximately 103sec−1and 1 sec−1. Some spectral features can be assigned to specific radical sites. For instance, electron adduct to disulfide is formed by the primary action of H atoms at pH 6.6, by the primary action of hydrated electrons at pH 7.6 and by intramolecular reaction of primary product formed by action of OH at

ISSN:0021-2148    

DOI:10.1002/ijch.197200113

出版商:WILEY‐VCH Verlag    

年代:1972

数据来源: WILEY

摘要:

AbstractThe separate contributions of the primary aqueous radicals to the changes in activity, molecular configuration and amino acid composition of RNase, produced by γ‐irradiation of dilute solutions, have been identified. The most effective radical for inactivation is the H atom. Additional molecular products are formed on irradiation of the enzyme. Amino acid analyses of the irradiation products show significant damage only to the aromatic and sulfur‐containing resi

ISSN:0021-2148    

DOI:10.1002/ijch.197200114

出版商:WILEY‐VCH Verlag    

年代:1972

数据来源: WILEY

摘要:

AbstractA study of the mechanism of aqueous trypsin inactivation by radiation was carried out by pulse radiolysis and steady irradiation in the presence of various scavengers. The initial products consist of OH radical and H atom adducts to tryptophan residues, and of electron adduct to cystine residues. Essentially, all OH react with trypophan with k(OH + trypsin) = (8.2 ± 1.2) × 1010M−1sec−1. The electron adduct to the disulphide bond accounts for about 60 per cent of the electron yield, with k(eaq+ trypsin) = (3.5 ± 0.8) × 1010M−1sec−1. Measurements of tryptophan residue loss and sulphydryl formation under different irradiation conditions show that the initial reactions are substantially reversible, except for the destruction of tryptophan under aerobic conditions. Many primary radicals induce inactivation with low independent probabilities, indicating that only a small fraction of the possible reaction sites for each species influence the integrity of the ac

ISSN:0021-2148    

DOI:10.1002/ijch.197200115

出版商:WILEY‐VCH Verlag    

年代:1972

数据来源: WILEY

摘要:

AbstractSome inorganic radical‐anions, which have very strong absorption spectra, have some oxidative reaction specificity with amino acids. Combined pulse radiolysis and inactivation studies on the reactions of these radicals with several enzymes lead to identification of amino acid residues essential to enzymic activity. Data are reviewed for the enzymes, lysozyme, ribonuclease, trypsin, α‐chymotrypsin, papain and carboxypeptidase. The reducing radical, CO2−, is more selective than the hydrated electron in its reactions with enzymes and proteins. Results from pulse radiolysis studies in electron‐transfer and other reactions involving CO2−are compared with results from inactivation studies with lysozyme and ri

ISSN:0021-2148    

DOI:10.1002/ijch.197200116

出版商:WILEY‐VCH Verlag    

年代:1972

数据来源: WILEY

摘要:

AbstractThe pulse radiolysis technique has been employed in the investigation of the dismutation of superoxide radicals, O−2and HO2, in the presence of superoxide dismutase in aqueous solutions. The decay of superoxide radicals in the presence of the enzyme was found to be first order in both enzyme and superoxide concentrations. An apparent second order reaction rate constant was found to be about 2 × 109M−1sec−1, decreasing slightly as the pH is increased from 5 to 9.5. A mechanism which accounts for all our observations is proposed. It includes two steps: (1) formation of a product (EO−2or E−) from one enzyme (E) molecule and one O−2radical ion; (2) regeneration of E by a reaction of this product with an additional O−2ion radical. The reaction rate constants k (E+O − 2)= (1.4 ± 0.2) × 109and k (E −(or EO − 2) + O − 2)= (1.9 ± 0.6) × 109M−1sec−1were measured at pH = 7

ISSN:0021-2148    

DOI:10.1002/ijch.197200117

出版商:WILEY‐VCH Verlag    

年代:1972

数据来源: WILEY