Christopher J. Kay

Mechanochemical mechanism for peptidyl free radical generation by amyloid fibrils

© 1997 Federation of European Biochemical Societies.

Measurement of oxidation-reduction midpoint potentials by room temperature electron paramagnetic resonance potentiometry☆

A room temperature electron paramagnetic resonance potentiometric cell has been developed for the measurement of oxidation-reduction midpoint potentials of enzymes containing paramagnetic centers. Based upon an aqueous flat cell designed for use with the Varian TM high sensitivity cavity, the apparatus combines a high degree of anaerobiosis with low volume requirements. The cell is simple in design, easily constructed, and can be adapted for use with most spectrometer cavities. Tests of the cell using xanthine oxidase, in 50 mM Bicine buffer, pH 7.7, yielded midpoint potentials of -345 and -371 mV for the Mo(VI)/Mo(V) and Mo(V)/Mo(IV) couples compared with values of -373 and -377 mV obtained by electron paramagnetic resonance analysis of frozen potentiometric samples. These values indicate that shifts, of the order of 20-40 mV, may occur upon freezing poised samples. For the Mo center of xanthine oxidase, these shifts in potential are more pronounced for the Mo(VI)/Mo(V) couple and result in a destabilization of the Mo(V) intermediate during freezing.

The Role of Quinone Pools in Regulating Electron Transport in Plant Mitochondria

The plant mitochondrial respiratory chain contains pathways of substrate oxidation not present in the mammalian counterpart. These differences include the ability to oxidiae cytosolic NAD(P)H via a dehydrogenase located on the outer face of the inner membrane; the oxidation of glycine by mitochondria from photosynthetic tissues; the oxidation of matrix NADH without energy conservation at site I1, and the cyanide resistant respiration present in many types of plant mitochondria2. The potential of plant mitochondria to oxidise a variety of substrates coupled to different degrees of energy conservation depending on the pathway used, makes it important to understand how these pathways are regulated, to be able to assess their likely significance in vivo.