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Biomedical subjects

L Ernster

Publications and source records attributed to L Ernster.

At least 73 records · Page 4Linked to original sources
PubMed1985

Cation-dependent reassembly of F0F1-ATPase in submitochondrial particles: evidence for a binding site for F1 on F0 in the absence of F6 and oligomycin sensitivity-conferring protein.

Bovine heart submitochondrial particles depleted of F1, OSCP (oligomycin sensitivity-conferring protein), and F6 require the presence of cations to rebind F1. Among the cations tested, NH4+, Cs+, and Rb+ were most efficient, followed by K+, Na+, Li+, Ca2+, and Mg2+. The extent of F1 binding approached that occurring upon supplementation with F6 and/or OSCP, and was similar to the F1 content of particles prior to depletion. In the absence of cations, F6 and/or OSCP were ineffective in promoting the binding of F1 to the depleted particles. The F1 bound to the particles in the presence of cations alone was completely insensitive to oligomycin. It remained bound to the particles after removal of the cation, and could be rendered partially (approximately 50%) or maximally (less than 80%) oligomycin-sensitive upon the subsequent addition of OSCP or of F6 and OSCP, respectively. The surface potential of the particles, as determined by microelectrophoresis, was screened by all cations tested, regardless of their ability to promote the binding of F1; this was in contrast to earlier findings with particles depleted of F1 only, where the ability of cations to promote the rebinding of F1 paralleled their efficiency to neutralize the surface charge of the particle membrane. It is concluded that the effect of cations on the binding of F1 to F1-, F6-, and OSCP-depleted particles is due to a specific interaction of the cations with certain segments or components of the membrane. The results suggest the existence of a binding site for F1 on F0 in addition to the binding site(s) provided by F6 and OSCP.

Ammonia↗
PubMed1985

Transport of Ca2+ and Mn2+ by mitochondria from rat liver, heart and brain.

The energy-dependent, respiration-supported uptake and the uncoupler- or Na+-induced release of Ca2+ and Mn2+ by mitochondria from rat liver, heart and brain were investigated, using as indicators radioisotopes (45Ca and 54Mn), proton ejection, oxygen consumption, nicotinamide nucleotide oxidation-reduction and, in the case of Ca2+, the metallochromic dye Arsenazo III. Ca2+ uptake in the presence of Pi was rapid in mitochondria from liver and brain, and less rapid in those from heart. Mn2+ uptake was much slower than that of Ca2+ in liver and heart, but only slightly slower in brain. When added together, Ca2+ accelerated the uptake of Mn2+, and Mn2+ retarded the uptake of Ca2+, by mitochondria from all three tissues. When Mn2+ was present during Ca2+ uptake, its own uptake remained accelerated even after Ca2+ uptake was terminated. Mg2+, which was not taken up, inhibited Ca2+ uptake by mitochondria from all three tissues, and, when present during Ca2+ uptake, accelerated the subsequent uptake of Mn2+. The uncoupler CCCP induced a release of both Ca2+ and Mn2+ from all three sources of mitochondria; yet, release of Mn2+ took place only in the absence of Pi. The release followed the same pattern as the uptake, i.e., Ca2+ accelerated the release of Mn2+ and Mn2+ retarded the release of Ca2+. Na+ induced a release of both Ca2+ and Mn2+ from heart and brain but not from liver mitochondria; again, Mn2+ release occurred only in the absence of Pi. The Na+-induced release of Ca2+ was inhibited by Mn2+, but the Na+-induced release of Mn2+ was not accelerated by Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Oligomycin sensitivity-conferring protein (OSCP) of beef heart mitochondria. Internal sequence homology and structural relationship with other proteins.

Structural analysis of oligomycin sensitivity-conferring protein (OSCP) revealed repeating sequences (residues 1-89, 105-190) suggesting an evolution of the protein by gene duplication. In addition to the reported homology with the delta-subunit of Escherichia coli F1ATPase, OSCP also shows a certain homology with the b-subunit of E. coli F0 and the ADP/ATP carrier of mitochondria.

Adenosine Triphosphatases↗
PubMed1984

Amino acid sequence of the oligomycin sensitivity-conferring protein (OSCP) of beef-heart mitochondria and its homology with the delta-subunit of the F1-ATPase of Escherichia coli.

The complete amino acid sequence of the oligomycin sensitivity-conferring protein (OSCP) of beef-heart mitochondria is reported. The protein contains 190 amino acids and has a molecular mass of 20 967. Its structure is characterized by a concentration of charged amino acids in the two terminal segments (N 1-77 and C 128-190) of the protein, whereas its central region is more hydrophobic. The earlier reported homology of the protein with the delta-subunit of E. coli F1, based on the terminal amino acid sequences of OSCP, is further substantiated.

Adenosine Triphosphatases↗
PubMed1984

The oligomycin sensitivity conferring protein (OSCP) of beef heart mitochondria: studies of its binding to F1 and its function.

The binding of "oligomycin sensitivity conferring protein" (OSCP) to soluble beef-heart mitochondrial ATPase (F1) has been investigated. OSCP forms a stable complex with F1, and the F1 X OSCP complex is capable of restoring oligomycin- and DCCD-sensitive ATPase activity to F1- and OSCP-depleted submitochondrial particles. The F1 X OSCP complex retains 50% of its ATPase activity upon cold exposure while free F1 is inactivated by 90% or more. Both free F1 and the F1 X OSCP complex release upon cold exposure a part--probably 1 out of 3--of their beta subunits; whether alpha subunits are also lost is uncertain. The cold-treated F1 X OSCP complex is still capable of restoring oligomycin- and DCCD-sensitive ATPase activity to F1- and OSCP-depleted particles. OSCP also protects F1 against modification of its alpha subunit by mild trypsin treatment. This finding together with the earlier demonstration that trypsin-modified F1 cannot bind OSCP indicates that OSCP binds to the alpha subunit of F1 and that F1 contains three binding sites for OSCP. The results are discussed in relation to the possible role of OSCP in the interaction of F1 with the membrane sector of the mitochondrial ATPase system.

Adenosine Triphosphatases↗
PubMed1984

Uncoupler-accelerated efflux of 5-hydroxytryptamine from platelets of healthy subjects and patients with unipolar and bipolar depression.

The efflux of 14C-5-hydroxytryptamine (5HT) from platelets of 25 depressed patients (16 unipolar and 9 bipolar) and 22 control subjects was studied in the presence of carbamyl cyanide m-chlorophenylhydrazone (FCCP), which dissipates H+ gradients. FCCP (0.31 microM), at 10 minutes' incubation time, enhanced the efflux of 14C-5HT to a significantly higher extent from platelets of patients with bipolar depression than from platelets of control subjects. An analysis of variance revealed a significant interaction between the diagnostic categories (unipolar, bipolar, and control) and sex in accounting for variation of the FCCP-evoked efflux. The diagnostic category X sex effect was also significant. The results reported indicate that the FCCP-evoked efflux of 5HT is an easily measured biochemical parameter of possible diagnostic interest.

Adult↗
PubMed1984

Influence of in vitro lactic acidosis and hypercapnia on respiratory activity of isolated rat brain mitochondria.

Respiratory activity and the ADP/O ratio of isolated rat brain mitochondria were measured following incubation with varying concentrations of lactic acid in reaction media buffered either with bicarbonate and CO2 or with phosphate alone, at a pH of 7.1. Increasing lactic acid levels caused a progressive decrease in substrate-, phosphate-, and ADP-stimulated (State 3) respiration and ADP/O ratios. Fifteen millimolar lactic acid, pH 6.4, caused approximately 50% inhibition of State 3 respiration (with malate + glutamate as substrate). At lower pH values (5.3-6.1), addition of ADP caused little or no increase in O2 consumption; i.e., ATP formation ceased. Addition of lactic acid at constant pH moderately affected respiratory control ratios but did not change State 3 respiration or ADP/O ratios. Thus, the effect of lactic acid was related to the pH change. Increasing CO2 concentrations in the reaction medium had similar effects on mitochondrial respiration, indicating that changes in extramitochondrial pH rather than in transmembrane H+ gradients determined the respiratory alterations. Following a 5-min incubation of mitochondria with lactic acid, pH 6.1, there was an incomplete recovery of State 3 respiration and respiratory control ratios. It is concluded that mitochondrial respiration is inhibited by a decrease in pH which, if excessive, may lead to a permanent suppression of ATP production. These results may, at least partly, explain the deleterious effects of enhanced lactic acidosis in brain ischemia.

Acidosis↗
PubMed1984

Mutagenicity of quinones: pathways of metabolic activation and detoxification.

The mutagenicity of various quinones, a class of compounds widely distributed in nature, is demonstrated in the Salmonella TA104 tester strain. The metabolic pathways by which four quinones, menadione, benzo[a]pyrene 3,6-quinone, 9,10-phenanthrenequinone, and danthron, caused mutagenicity in this test system were investigated in detail as were the detoxification pathways. The two-electron reduction of these quinones by NAD(P)H-quinone oxidoreductase (DT-diaphorase) was not mutagenic, whereas the one-electron reduction, catalyzed by NADPH-cytochrome P-450 reductase, was mutagenic, except for danthron, which was only slightly mutagenic. The mutagenicity of the quinones via this pathway was found to be attributable to the generation of oxygen radicals. The cytochrome P-450 monooxygenase also played a significant role in the detoxification and bioactivation of these quinones. For example, phenanthrenequinone was converted to a nonmutagenic metabolite in a cytochrome P-450-dependent reaction, whereas danthron was converted to a highly mutagenic metabolite. These studies show the complexity of metabolic pathways involved in the mutagenicity of quinones.

Animals↗
PubMed1984

Induction of cytosolic glutathione transferase and microsomal epoxide hydrolase activities in extrahepatic organs of the rat by phenobarbital, 3-methylcholanthrene and trans-stilbene oxide.

The effects of treating male Sprague-Dawley rats with phenobarbital, 3-methylcholanthrene or trans-stilbene oxide on cytosolic glutathione transferase and microsomal epoxide hydrolase activities in the liver, intestine, kidney, lung, testis, adrenal, spleen, heart and brain have been investigated. Studies on the time-courses of induction in liver demonstrate that these are complete after five days' treatment at the doses used. Phenobarbital induces both cytosolic glutathione transferase and microsomal epoxide hydrolase activities significantly only in liver and intestine. 3-Methylcholanthrene induces these activities in liver only. Trans-Stilbene oxide induces both of these activities in liver and kidney, and cytosolic glutathione transferase activity in adrenal as well.

Animals↗
PubMed1983

Lack of ability of trypsin-treated mitochondrial F1-ATPase to bind the oligomycin-sensitivity conferring protein (OSCP).

Soluble beef-heart mitochondrial F1-ATPase modified in its alpha-subunit by mild trypsin treatment (alpha'-F1) can no longer bind oligomycin-sensitivity conferring protein (OSCP) but is still capable of binding to F1-depleted submitochondrial particles, giving rise to a maximally oligomycin-sensitive ATPase, provided the particles contain their native complement of OSCP. When OSCP is removed from the particles, alpha'-F1 can still bind to the particles, but added OSCP induces only a low degree of oligomycin sensitivity. The possible role of OSCP in the functional coupling of the catalytic (F1) and H+-translocating (Fo) moieties of mitochondrial ATPase is discussed. The results suggest a functional similarity between the OSCP component of mitochondrial ATPase and the delta-subunit of E. coli ATPase, which is in accordance with the structural homology recently found to exist between the two polypeptides.

Adenosine Triphosphatases↗
PubMed1983

Cation requirement for the reconstitution of oligomycin-sensitive ATPase by means of soluble F1-ATPase and F1-depleted submitochondrial particles.

Bovine heart submitochondrial particles depleted of F1 by treatment with urea ("F1-depleted particles') were incubated with soluble F1-ATPase. The binding of F1 to the particles and the concomitant conferral of oligomycin sensitivity on the ATPase activity required the presence of cations in the incubation medium. NH4+, K+, Rb+, Na+ and Li+ promoted reconstitution maximally at 40-74 mM, guanidinium+ and Tris+ at 20-30 mM, and Ca2+ and Mg2+ at 3-5 mM. The particles exhibited a negative zeta-potential, as determined by microelectrophoresis, and this was neutralized by mono- and divalent cations in the same concentration range as that needed to promote F1 binding and reconstitution of oligomycin-sensitive ATPase. It is concluded that the cations act by neutralizing negative charges on the membrane surface, mainly negatively charged phospholipids. These results are discussed in relation to earlier findings reported in the literature with F1-depleted thylakoid membranes and with submitochondrial particles depleted of both F1 and the coupling proteins F6 and oligomycin sensitivity-conferring protein.

Adenosine Triphosphatases↗
PubMed1983

Mn2+ prevents the Ca2+-induced inhibition of ATP synthesis in brain mitochondria.

Uptake of Ca2+ by rat brain mitochondria causes an inhibition of respiratory stimulation by ADP, and the inhibition is relieved upon Na+-induced release of Ca2+ from the mitochondria, in accordance with earlier reports. We show that simultaneous uptake of Ca2+ and Mn2+ results in no inhibition of ADP-stimulated respiration, indicating that Mn2+ prevents the Ca2+-induced inhibition of ATP synthesis, without preventing Ca2+ accumulation in the mitochondria. The results are discussed in relation to a possible involvement of the mitochondrial ATPase-inhibitor protein in the observed effects of Ca2+ and Mn2+.

Adenosine Diphosphate↗
PubMed1983

Respiratory activity of isolated rat brain mitochondria following in vitro exposure to oxygen radicals.

Respiratory activity of isolated rat brain mitochondria was measured following in vitro exposure to oxygen radicals. The radicals were generated by hypoxanthine and xanthine oxidase in the presence of a suitable iron chelate and caused a severe inhibition of respiration stimulated by phosphate plus ADP (with malate + glutamate as substrate). The damage could be prevented by catalase or high concentrations of mannitol, but not by superoxide dismutase. A similar effect was observed when hypoxanthine and xanthine oxidase were replaced by glucose and glucose oxidase or by hydrogen peroxide. Most of the findings indicate that the hydroxyl radical is the damaging agent. It is concluded that brain mitochondria exposed to oxygen radicals in vitro show an inhibition of respiratory activity similar to that reported by other investigators as occurring in mitochondria in vivo following transient cerebral ischemia. Therefore, oxygen radicals may contribute to this type of cell damage.

Animals↗
PubMed1982

Characterization of the microsomal cytochrome P-450 species induced in rat liver by trans-stilbene oxide.

trans-Stilbene oxide differs from the classical inducers of drug-metabolizing enzymes, phenobarbital and 3-methylcholanthrene, in that it induces the so-called phase II activities, epoxide hydrolase and glutathione S-transferase, to a much larger extent than it induces cytochrome P-450. Nonetheless, the level of cytochrome P-450 in liver microsomes from rats treated with trans-stilbene oxide is increased significantly to twice the control value. The existence of a number of different isozymes of cytochrome P-450 has now been clearly demonstrated and in the present study we have posed the question. What form(s) of cytochrome P-450 is induced by trans-stilbene oxide? A number of criteria including substrate specificity, pattern of benzo(a)pyrene metabolism, sensitivity to inhibitors, substrate binding spectra, ethylisocyanide binding spectra, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and crossed immunoelectrophoresis were used to answer this question. It seems clear that trans-stilbene oxide induces the same form(s) of cytochrome P-450 as phenobarbital.

7-Alkoxycoumarin O-Dealkylase↗