Estimation of redox properties of chemical compounds by their reactions with free radicals.

The electron-donor and electron-acceptor properties of biologically active compounds were estimated on the basis of their reactions with free radical intermediates of the excited dye eosin. After dye excitation by a short flash of light, the kinetics of dye anion radicals in the pure dye solution were compared with those in the presence of the natural reducing agent NADH or a number of substances which are known as local anesthetics (LA). LA individually slowed the decay of dye anion radicals and enhanced their concentration to a lesser extent than NADH, thus acting as electron donors toward dye radicals. The electron-donor properties of LA studied correlate with their ability to block sodium channels. In contrast, the sodium channel agonist veratridine decreased the concentration of dye anion radicals, thus showing electron-acceptor properties. The opposite redox features of the channel antagonist and the agonist were revealed also by a modified method suitable for steady-light spectroscopy. Promoted by NADH, eosin photobleaching was slowed by the electron acceptor ferricyanide as well as by veratridine and some phenols. The electron-acceptor properties of the latter compounds correlated with their ability to inhibit ATP synthesis by submitochondrial particles. Thus, these methods may be used to evaluate the redox properties of compounds not characterized by electrochemical methods and to predict their biological activity.

Ca2+ transport in mitochondria of the ciliate protozoan Tetrahymena pyriformis.

Mitochondria isolated from the late-exponential non-shaken culture of the ciliate protozoan Tetrahymena pyriformis GL was investigated. The presence of energy-dependent Ca2+ transport system was shown. In the main the properties of this system have been essentially the same as in mitochondria of vertebrate organisms. The isolated mitochondria contained 23 +/- 5 ng-ion Ca2+ per mg of protein. The intramitochondrial free concentration of Ca2+ was measured in the presence of uncoupler FCCP with the use of fluorescent Ca2+ chelator chlortetracycline and null point titration method. In the absence of phosphate, free [Ca2+] varied from 1 to 2.5 mM depending on the internal Ca2+ content. In the presence of 2 mM phosphate, free [Ca2+]in has not exceeded 0.1-0.3 mM. It was shown that ruthenium red and Mg2+ in different manner have an inhibitory effect on Ca2+ transport. Besides this, Mg2+ also has a stabilizing effect on mitochondria, possibly, by preventing passive ions leaks across the membrane.