[Kinetic and structural characteristics of succinate dehydrogenase components reacting with natural and artificial electron acceptors]. / Kineticheskie i strukturnye kharakteristiki komponentov suktsinatdegidrogenazy, reagiruiushchikh s estestvennym i iskusstvennymi aktseptorami élektronov

A new catalitic activity of soluble succinate dehydrogenase, i.e. the reduction of low (20-200 muM) concentration of ferricyanide in the presence of succinate is described. The apparent Km value for the acceptor is about 200 muM. The turnover numbers of the enzyme measured in this reaction, with PMS as an electron acceptor and in the system reconstituted from soluble enzyme and alkali-treated submitochondrial particles (succinate oxidase) are found to be almost the same. The new succinate. ferricyanide reductase activity is very sensitive to oxygen, high (3 mM) ferricyanide concentration and mercaptide-forming agents. When the enzyme is stored under aerobic conditions the loss of this activity occurs according to the first-order kinetics with the same rate constants as the reconstitutive activity decreases. The rate constants both for ferricyanide reductase and reconstitution decay do not depend on pH within the range of 6,5--7,5 (k = 8.10(-2) min-1) and increase dramatically at pH 8,5 (K = 4.10(-1) MIN-1). When these two activities are lost after oxygen exposure the PMS-reductase fall down to about 50% of its original activity. The new ferricyanide reductase is found only in the soluble preparation of the enzyme succinate: cytochrome c reductase, succinate dehydrogenase of submitochondrial particles and reconstituted succinate oxidase do not interact with low concentrations of ferricyanide. The treatment of the enzyme after inactivation by oxygen exposure with sulfide ion--iron--mercaptoethanol mixture followed by Sephadex filtration completely restores the original reconstitutive, ferricyanide and PMS reductase activities. The hypothesis is suggested that succinate dehydrogenase contains at least two red-ox centers reacting with electron acceptors. The first one is located in hydrophylic environment (mitochondrial matrix) being accessible for high concentrations of ferricyanide. The second one (iron--sulfur complex, Hipip-type) is responsible for ferricyanide reductase activity described, being located intramembraneously and involved in the electron transfer between dehydrogenase and the rest of the respiratory chain.

[Various properties of the creatine transport system and the location of creatine kinase in skeletal muscle mitochondria]. / Nekotorye svoistva transportnoi sistemy kreatina i lokalizatsiia kreatnikinazy v mitokhondriiakh skerltnykh myshts

Water and creatine contents were studied in rat skeletal muscle mitochondria after their 5 min. incubation in creatine solutions, pH 7.2 or 8.4. The content of water and creatine in mitochondria was found to be higher at pH 8.4, than at pH 72, the creatine content correlated with the water content. Structural creatine analogues, containing aminogroups with pKa greater than or equal to 9.5 or carboxyl groups, inhibited the infusion of creatine into mitochondria more strongly than substances having aminogroups with pKa less than 5. The penetrating form is creatine amphiion; the effect of pH on the permeability is probably due to the activation of the creatine transmitter. Rat skeletal muscle mitochondria contain creatine kinase at both sides of the inner membrane. This conclusion is based on the fact that under conditions, supplying the direct course of the creatine kinase reaction (the incubation medium contains Ca2+ and creatine; pH 7.8), ADP produces the stimulation of mitochondrial respiration up to the oxygen exhausting in a polarographic unit. Similarly, ADP irreversibly stimulates mitochondrial respiration in the presence of 1 mM EDTA, if EDTA and ADP are added after the preincubation of mitochondria in creatine-containing medium and after accumulating small amounts of Ca2+ by mitochondria.