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Kinetics and free energy profiles of spermine transport in liver mitochondria
No full textIn the present study, the voltage-dependent mechanism of spermine transport in liver mitochondria [Toninello, A., Dalla Via, L., Siliprandi, D., and Garlid, K. D. (1992) J. Biol. Chem. 267, 18393−18397] was further characterized by determining the rate constants Jmax and Km as functions of membrane potential. An increase in mitochondrial membrane potential from 150 to 210 mV promoted spermine transport, as reflected by an approximate 4-fold increase in Jmax and 25% decrease in Km. The mechanism for the voltage dependence of transport was examined using the β value, i.e., the slope of ln(flux) vs FΔΨ/RT plots. Flux-voltage analyses performed at very high and very low spermine concentrations yielded β values of 0.125 and 0.25, for Jmax and Jmax/Km, respectively. The physical significance of these β values was analyzed by means of a theory relating the enzyme reaction rate to the free energy profiles [Yagisawa, S. (1985) Biochem. J. 303, 305−311]. Depending on the nature of Km, two possible models could be proposed to describe the location and shape of the barriers in the membrane. Analysis of previous data concerning spermine binding [Dalla Via, L., Di Noto, V., Siliprandi, D., and Toninello, A. (1996) Biochim. Biophys. Acta 1284, 247−252] by a new rationale provided evidence for an asymmetrical energy profile composed of two peaks with the binding site near the membrane surface followed by a rate-determining energy barrier for the movement of the bound spermine toward the internal region of the membrane
Have mammalian amine oxidases and mitochondrial polyamine transporter a similar protein structure?
No full textInteraction of genistein with the mitochondrial electron transport chain results in opening of the membrane transition pore
No full textGenistein, a natural isoflavone present in soybeans, is a potent agent in the prophylaxis and treatment of cancer. Addition of genistein to isolated rat liver mitochondria (RLM) induces swelling, loss of membrane potential and release of accumulated Ca2+. These changes are Ca2+-dependent and are prevented by cyclosporin A (CsA) and bongkrekic acid (BKA), two classical inhibitors of the mitochondrial permeability transition (MPT). Induction of the MPT by genistein is accompanied by oxidation of thiol groups and pyridine nucleotides. The reducing agent dithioerythritol and the alkylating agent N-ethylmaleimide (NEM) completely prevent the opening of the transition pore, thereby emphasizing that the effect of the isoflavone correlates with the mitochondrial redox state. Further analyses showed that genistein induces the MPT by the generation of reactive oxygen species (ROS) due to its interaction with the respiratory chain at the level of mitochondrial complex III
Uptake of spermine by rat liver mitochondria and its influence on the transport of phosphate.
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