Backbone dynamics of the channel-forming antibiotic zervamicin IIB studied by 15N NMR relaxation

The backbone dynamics of the channel-forming peptide antibiotic zervamicin IIB (Zrv-IIB) in methanol were studied by 15N nuclear magnetic resonance relaxation measurements at 11.7, 14.1 and 18.8 T magnetic fields. The anisotropic overall rotation of the peptide was characterized based on 15N relaxation data and by hydrodynamic calculations. 'Model-free' analysis of the relaxation data showed that the peptide is fairly rigid on a sub-nanosecond time-scale. The residues from the polar side of Zrv-IIB helix are involved in micro-millisecond time-scale conformational exchange. The conformational exchange observed might indicate intramolecular processes or specific intermolecular interactions of potential relevance to Zrv-IIB ion channel formation.

Proteinaceous complexes from mitochondrial contact sites

A Triton X-100 extract from rat brain mitochondria was obtained using low detergent/protein ratio. From this extract a proteinaceous complex was purified; its molecular weight was as high as 880 kD. The complex contained both hexokinase and creatine kinase activity. When incorporated into phospholipid bilayer membranes, the complex formed a channel whose activity was different than the channel activity of purified porin isolated either by adsorption chromatography or by dissociation from protein complexes. A ligand of the mitochondrial benzodiazepine receptor (Ro5-4864) in submicromolar concentrations had an apparent influence on the kinetic behavior of enzymatic coupling of hexokinase and creatine kinase. It is suggested that the 880-kD complex is formed by mitochondrial contact sites. The role of the isolated protein complex in the formation of nonspecific permeability in mitochondria is discussed.

The permeability transition pore induced under anaerobic conditions in mitochondria energized with ATP

The role of oxygen in the induction of mitochondrial permeability transitions was studied. Oxygen consumption, swelling, membrane potential and calcium transport were recorded simultaneously in isolated rat liver mitochondria. Oxygen depletion was accomplished by saturating the medium with N2 and allowing either mitochondrial respiration or glucose/glucose oxidase to consume the residual oxygen. Upon anaerobiosis, mitochondria were supplemented with 500 microM ATP to support succinate-driven membrane potential. Under these conditions, 100 microM Ca2+ induced cyclosporin A-sensitive permeability transitions. To eliminate the possible inhibition of permeability transition by high concentrations of adenine nucleotides, anaerobic mitochondria were also energized by the combination of 20 microM ADP and phosphoenolpyruvate/pyruvate kinase. These mitochondria also underwent Ca2+-induced permeability transition. Under both of these conditions, namely the addition of ATP as a single or through actions of pyruvate kinase, the respiratory components were totally reduced. Thus, oxygen is not a necessary factor for mitochondria to undergo permeability transitions.