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J E Frew

Publications and source records attributed to J E Frew.

8 recordsLinked to original sources
PubMed1993

EPR and ENDOR detection of compound I from Micrococcus lysodeikticus catalase.

We present the first EPR and ENDOR examination of a catalase compound I (Cat I), the one formed by peracetic acid treatment of Micrococcus lysodeikticus catalase. The Cat I rapid-passage EPR signal (g perpendicular eff = 3.32; g parallel eff approximately 2) appears quite different from those reported previously for the compounds I from horseradish peroxidase (HRP I) and chloroperoxidase. Nonetheless, all three signals can be explained by the same model for exchange coupling between an S = 1 oxoferryl [Fe = O]2+ moiety and a porphyrin pi-cation radical (S' = 1/2) (Schulz, C. E., et al. (1979) FEBS Lett. 103, 102-105). The signal for Cat I is unlike those for the two peroxidases in that it reflects a ferromagnetic rather than antiferromagnetic exchange. Preliminary 1H ENDOR spectra for Cat I appear to differ from the proton (1H) ENDOR spectra of HRP I; the latter, along with the 14N ENDOR spectra, indicate that the porphyrin radical in HRP I exhibits a predominantly A2u-like state having large spin densities on porphyrin N and C(beta). The proton ENDOR spectrum of Cat I is insensitive to H/D exchange, which indicates that the [Fe = O]2+ moiety is not protonated. Consideration of the EPR results for a series of compounds I suggests that the sign and magnitude of the exchange parameter (J) is correlated with the nature of the proximal axial ligand.

Catalase↗
PubMed1990

Analysis of transference in Gestalt group psychotherapy.

In Gestalt therapy, transference is viewed as a contact boundary disturbance which impairs the patient's ability to accurately perceive the present therapy situation. The boundary disturbances in Gestalt therapy most closely related to the analytic notion of transference are projection, introjection, and confluence. In Gestalt group psychotherapy, group members interfere with the process of need identification and satisfaction by distorting their contact with each other through projecting, introjecting, and being confluent. The Gestalt group therapist uses interventions directed to individuals and to the group to increase participants' awareness of these boundary disturbances and of the present contact opportunities available to them when these disturbances are resolved. In formulating interventions, the leader is mindful of the function of boundary disturbances to the group-as-a-whole as well as to individuals.

Gestalt Therapy↗
PubMed1988

Direct and indirect electron transfer between electrodes and redox proteins.

The direct electrochemistry of redox proteins has been achieved at a variety of electrodes, including modified gold, pyrolytic graphite and metal oxides. Careful design of electrode surfaces and electrolyte conditions are required for the attainment of rapid and reversible protein-electrode interaction. The electron transfer reactions of more complex systems, such as redox enzymes, are now being examined. The 'well-behaved' electrochemistry of redox proteins can be usefully exploited by coupling the electrode reaction to enzymes for which the redox proteins act as cofactors. In systems where direct electron transfer is very slow, small electron carriers, or mediators, may be employed to enhance the rate of electron exchange with the electrode. The organometallic compound ferrocene and its derivatives have proved particularly effective in this role. A new generation of electrochemical biosensors employs ferrocene derivatives as mediators.

Electrodes↗
PubMed1987

Electron-transfer biosensors.

The electrochemistry of redox proteins is now well established. Conditions exist which allow electron-transfer reactions of all simple proteins to proceed rapidly and reversibly at electrodes. Coupling of the electrode reaction to enzymes, for which the redox proteins act as cofactors, allows exploitation of this good electrochemistry. This is well illustrated by the enzyme-catalysed electrochemical oxidation of p-cresol to p-hydroxybenzaldehyde, which has been shown to proceed along with coupling to the electrode via the copper protein, azurin, or the organometallic compound ferroceneboronic acid. Ferrocene derivatives, in general, show a degree of versatility, coupling the electron-transfer reactions of many enzymes. Thus derivatives of the ferricinium ion act as excellent electron-transfer reagents from the enzyme glucose oxidase. The system is capable of detecting glucose in blood. Similar procedures, in conjunction with the appropriate enzyme, have yielded assays for, among others, H2O2 and cholesterol.

Biotechnology↗
PubMed1983

Kinetics of yeast cytochrome c peroxidase compound I formation with modified substrates (peroxybenzoic acids).

The kinetics of formation of Compound I of yeast cytochrome c peroxidase (ferrocytochrome c:hydrogen-peroxide oxidoreductase, EC 1.11.1.5) with a series of peroxybenzoic acids were studied. Reactivity is affected not only by protein ionization, as in the reaction with H2O2, but also by substrate ionization. The reactivity of negatively charged substrates is markedly lower than that of uncharged species, implying that electrostatic factors profoundly influence substrate binding. The rate constants for neutral peroxybenzoic acids carrying electron-withdrawing substituents increase with increasing peroxy acid pKa. This behaviour suggests that, as previously discussed for reactions of turnip peroxidases, formation of peroxy anion by ionization of substrate within the active site is kinetically important. The results support the mechanism of cytochrome c peroxidase Compound I formation which has been proposed by Poulos and Kraut (J. Biol. Chem. 225 (1980), 8199-8205) on the basis of enzyme structural studies.

Benzoates↗