Effect Of 1-(p-methoxybenzyl)-6,7-methylenedioxyisoquinoline On Mitochondrial Respiration

[No abstract available]271015051507Vercesi, Magalhaes, Meirelles, (1975) ICRS Medical Sci., 3, p. 492Papa, de Gomez-Puyou, Gómez-Puyou, (1975) Eur. J. Biochem., 55, p. 1Lotina, Gómez-Puyou, Tuena de Gómez-Puyou, Chavez, (1973) Archs Biochem. Biophys., 159, p. 517Peña, Chavez, Carabez, Tuena de Gómez-Puyou, (1977) Archs Biochem. Biophys., 180, p. 522Sumner, (1944) Science, N.Y., 100, p. 413Ernster, Dallner, Azzone, (1963) J. biol. Chem., 238, p. 1124Burgos, Redfearn, The inhibition of mitochondrial reduced nicotinamide-adenine dinucleotide oxidation by rotenoids (1965) Biochimica et Biophysica Acta (BBA) - Enzymology and Biological Oxidation, 110, p. 475Gutman, Singer, Casida, (1970) J. biol. Chem., 245, p. 1992Pressman, (1963) J. biol. Chem., 238, p. 401Carafoli, (1974) Biochem. Soc. Symp., 39, p. 8

Binding Of Adenine Nucleotides To The F1-inhibitor Protein Complex Of Bovine Heart Submitochondrial Particles

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The binding of ATP radiolabeled in the adenine ring or in the γ- or α-phosphate to F1-ATPase in complex with the endogenous inhibitor protein was measured in bovine heart submitochondrial particles by filtration in Sephadex centrifuge columns or by Millipore filtration techniques. These particles had 0.44 ± 0.05 nmol of F1 mg-1 as determined by the method of Ferguson et al. [(1976) Biochem. J. 153, 347]. By incubation of the particles with 50 μM ATP, and low magnesium concentrations (<0.1 μM MgATP), it was possible to observe that 3.5 mol of [γ-32P] ATP was tightly bound per mole of F1 before the completion of one catalytic cycle. With [γ-32P]ITP, only one tight binding site was detected. Half-maximal binding of adenine nucleotides took place with about 10 μM. All the bound radioactive nucleotides were released from the enzyme after a chase with cold ATP or ADP; 1.5 sites exchanged with a rate constant of 2.8 s-1 and 2 with a rate constant of 0.45 s-1. Only one of the tightly bound adenine nucleotides was released by 1 mM ITP; the rate constant was 3.2 s-1. It was also observed that two of the bound [γ-32P]ATP were slowly hydrolyzed after removal of medium ATP; when the same experiment was repeated with [α-32P] ATP, all the label remained bound to F1, suggesting that ADP remained bound after completion of ATP hydrolysis. Particles in which the natural ATPase inhibitor protein had been released bound tightly only one adenine nucleotide per enzyme. The results indicate that one of the first events that occurs during ATP hydrolysis by the F1-inhibitor protein complex is the binding of two to three adenine nucleotides to sites that apparently are not hydrolytic. In addition, it was found that in the complex, the affinity of two to three of its adenine nucleotide binding sites is higher than in particulate enzymes devoid of the inhibitor protein. © 1992 American Chemical Society.3125578457902013/02203-6; FAPESP; São Paulo Research Foundation; 2014/00372-8; FAPESP; São Paulo Research FoundationFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Effect of Monovalent Cations on Na+/Ca2 Exchange and ATP-Dependent Ca2+Transport in Synaptic Plasma Membranes

Two Ca2+ transport systems were investigated in plasma membrane vesicles isolated from sheep brain cortex synaptosomes by hypotonic lysis and partial purification. Synaptic plasma membrane vesicles loaded with Na+ (Na+i) accumulate Ca2+ in exchange for Na+, provided that a Na+ gradient (in2192out) is present. Agents that dissipate the Na+ gradient (monensin) prevent the Na+/Ca2+ exchange completely. Ca2+ accumulated by Na+/Ca2+ exchange can be released by A 23187, indicating that Ca2+ is accumulated intravesicularly. In the absence of any Na+ gradient (K+i-loaded vesicles), the membrane vesicles also accumulate Ca2+ owing to ATP hydrolysis. Monovalent cations stimulate Na+/Ca2+ exchange as well as the ATP-dependent Ca2+ uptake activity. Taking the value for Na+/Ca2+ exchange in the presence of choline chloride (external cation) as reference, other monovalent cations in the external media have the following effects: K+ or NH4+ stimulates Na+/Ca2+ exchange; Li+ or Cs+ inhibits Na+/Ca2+ exchange. The ATP-dependent Ca2+ transport system is stimulated by increasing K+ concentrations in the external medium (Km for K+ is 15 mM). Replacing K+ by Na+ in the external medium inhibits the ATP-dependent Ca2+ uptake, and this effect is due more to the reduction of K+ than to the elevation of Na+. The results suggest that synaptic membrane vesicles isolated from sheep brain cortex synaptosomes possess mechanisms for Na+/Ca2+ exchange and ATP-dependent Ca2+ uptake, whose activity may be regulated by monovalent cations, specifically K+, at physiological concentrations

EFFECT OF TEMPERATURE AND IONOPHORES ON THE PERMEABILITY OF SYNAPTOSOMES

Synaptosomes swell rapidly in isosmotic solutions of glycerol or urea, but the swelling in solutions of larger non-electrolytes, such as erythritol, glucose or sucrose is slower. The permeability of synaptosomes to non-electrolytes is temperature dependent, and the low activation energies for the permeation of urea (13 kcal/mol) and erythritol (9.5 kcal/mol) indicate that the penetration of non-electrolytes into the synaptosomes does not imply complete dehydration of the molecules. The relative permeability of synaptosomes to cations, as measured by the rate of swelling in isosmotic solutions of acetate salts is in the order: NH+4 > Na+ > Li+ > K+ > Ca2+. The ionophores, X-537A and nigericin, or valinomycin + FCCP, which promote exchange of cations for H+, cause swelling of synaptosomes in solutions of potassium salts of acetate or propionate, but not in KCI, whereas H+ release is higher in KCI medium. This suggests that the organic unions cross the membrane after combining with H+ to form the respective weak acids. The relative permeability to anions is in the order: acetate 2243 propionate > Cl2212 > SO2-42243 maleate 2243 succinate. The energies of activation for the permeability of synaptosomes to potassium acetate in the presence of X-537A or gramicidin D are 13 kcal/mol and 7.5 kcal/mol, respectively, which reflects different mechanisms of action for the two ionophores in the membranes