Redox properties of b-type cytochromes in Escherichia coli and rat liver mitochondria and techniques for their analysis

We describe here apparatus and procedures for conducting potentiometric titrations and for analyzing the collected data in terms of the number of components present, their amounts and their midpoint potentials. Using these procedures we have determined the presence of three forms of cytochrome b₁ in Escherichia coli with midpoint potentials at pH 7.1 of about ?50, +110 and +220 mV. We were not able to demonstrate a change in any of these potentials by the addition of phosphate, ATP, or 2,4-dinitrophenol. We have been able to confirm the presence of two forms of cytochrome b in non-energized mitochondria and the apparent conversion of the low-potential component to a new high potential component upon energization of the mitochondria. However we cite further experimental data that question the actual conversion of one form of cytochrome b to another. An alternative interpretation based on our analysis suggests that the high voltage component may be present in a masked form in the non-energized mitochondria.     

CO-binding pigments and the functional terminal oxidase of the trypanosomatid hemoflagellate Crithidia fasciculata

CO-difference absorbance spectra of both intact cells and of mitochondrial preparations isolated from Crithidia fasciculata were obtained after anaerobiosis was attained either with substrates or with dithionite. Under both sets of conditions, the CO-difference spectrum of cytochrome a₃, with difference absorbance maxima at 430 and 589 nm and minima at 443 and 612 nm, was readily identified in both the intact cells and in the mitochondria. In addition to the difference absorbance bands of cytochrome a₃-CO, three difference absorbance maxima at 417, 538 and 570 nm and a minimum at 556 nm were observed. The magnitude of the maximum at 570 nm relative to the maximum of cytochrome a₃-CO at 589 nm was less for mitochondria rendered anaerobic with substrate than for mitochondria rendered anaerobic with dithionite. This difference was taken to define operationally two groups of mitochondrial CO-binding pigments: Group I is that group observed on anaerobiosis with substrate: Group II is the additional group observed on anaerobiosis with dithionite. The Group I CO-binding pigments were virtually absent from submitochondrial particles derived by sonication, but the Group II pigments remained.Photochemical action spectra were obtained with isolated mitochondria and intact cells to ascertain if cytochrome o was present. These action spectra, obtained in CO plus O₂ atmospheres, had maxima only at 432, 550 and 588 nm, attributable to the photodissociation of cytochrome a₃-CO. Even after suppression of cytochrome a₃ activity to 10% of the normal value, no contribution of cytochrome o activity to the photochemical action spectrum was observed. Cytochrome a₃ is therefore the only functional terminal oxidase present in the mitochondria of Crithidia fasciculata.     

The influence of cellular amino acids and the Na+: K+ pump on the membrane potential of the Ehrlich ascites tumor cell

The membrane potential of the Ehrlich ascites tumor cell was shown to be influenced by its amino acid content and the activity of the Na⁺: K⁺ pump. The membrane potential (monitored by the fluorescent dye, 3,3′-dipropylthiodicarbocyanine iodide) varied with the size of the endogenous amino acid pool and with the concentration of accumulated 2-aminoisobutyrate. When cellular amino acid content was high, the cells were hyperpolarized; as the pool declined in size, the cells were depolarized. The hyperpolarization seen with cellular amino acid required cellular Na⁺ but not cellular ATP. Na⁺ efflux was more rapid from cells containing 2-aminoisobutyrate than from cells low in internal amino acids. These observations indicate that the hyperpolarization recorded in cells with high cellular amino acid content resulted from the electrogenic co-efflux of Na⁺ and amino acids.Cellular ATP levels were found to decline rapidly in the presence of the dye and hence the influence of the pump was seen only if glucose was added to the cells. When the cells contained normal Na⁺ (approx. 30 mM), the Na⁺: K⁺ pump was shown to have little effect on the membrane potential (the addition of ouabain had little effect on the potential). When cellular Na⁺ was raised to 60 mM, the activity of the pump changed the membrane potential from the range ?25 to ?30 mV to ?44 to ?63 mV. This hyperpolarization required external K⁺ and was inhibited by ouabain.     

Function and properties of a soluble c-type cytochrome c-551 in secondary photosynthetic electron transport in whole cells of Chromatium vinosum as studied with flash spectroscopy

Changes in the absorption spectrum induced by 10-μs flashes and continuous light of various intensities were studied in whole cells of Chromatium vinosum.This paper describes the role and function of a soluble c-type cytochrome, c-551, which was surprisingly found to act in many ways similar to the cytochrome c-420 in Rhodospirillum rubrum, described in a previous paper [1].After the photooxidation of the membrane bound high potential cytochrome c-555 by a 10-μs flash, (the low potential cytochrome c-552 was kept permanently in the oxidized state) the oxidation of c-551 is observed ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.3}\text{ms}$). From a careful analysis of the absorbance difference spectrum and the kinetics it is concluded that there is approximately 0.6–0.7 c-551 per reaction center and that essentially all the c⁺-555 is reduced via the cytochrome c-551. The oxidized-reduced difference spectrum of c-551 shows peaks at 551 and 421.5 nm. The reduction of c⁺-551 following the flash-induced oxidation is strongly inhibited by HOQNO, but only slightly by antimycin A.Cytochrome c-551 reduces only the oxidized high potential cytochrome c-555, which is probably located on the outside of the membrane, on the opposite side of the primary acceptor. The low potential cytochrome c-552 does not show any detectable interaction with cytochrome c-551. After the cells have been sonicated, no c-551 is photooxidized and at least part of the cytochrome occurs in the solution.Analysis of the reduction kinetics of c⁺-551 in the absence and presence of external donors suggests that c⁺-551 is partly reduced via a cyclic pathway, which is blocked by addition of o-phenanthroline, and partly via a non-cyclic pathway. The non-cyclic reduction rate of c⁺-551 (k = 6 s^?1) is increased approximately 5–10 times upon thiosulphate addition, suggesting a role for c-551 between the final donor pool and the oxidized membrane bound c-type cytochromes.     

The involvement of sarcotubular membranes in genetic muscular dystrophy

Microsomal preparations from breast muscle of normal and dystrophic chickens are characterized with regard to ultrastructural features, protein composition, Ca²⁺ transport and ATPase activity.Dystrophic muscle yields a greater microsomal dry weight, with a reduced protein to lipid ratio. This is related to the presence of a considerable number of low density microsomes, in addition to seemingly normal microsomes. The low density microsomes display a reduced number of protein particles on freeze fracture faces.Electrophoretic analysis reveals nearly identical patterns in normal and dystrophic microsomes. Furthermore, normal and dystrophic microsomes sustain equal rates of Ca²⁺ transport and ATPase, demonstrating an identical protein specific activity. However, the dystrophic microsomes have a lower capacity to retain transported Ca²⁺.The high yield of low density microsomes with reduced capacity for Ca²⁺ uptake is attributed to the presence of membranes proliferated in the junctional and tubular sarcomere regions of the dystrophic muscle. It is suggested that proliferation of such membranes accounts for the altered excitation-contraction coupling and cable properties of genetically dystrophic muscle.     

Ca2+ and Mn2+ mediated binding of the glycoprotein peroxidase to membranes of Pharbitis cotyledons

Ca²⁺ and Mn²⁺ promote the binding of the basic isoperoxidase to a crude membrane preparation in extracts from Pharbitis cotyledons. The Ca²⁺- or Mn²⁺-induced binding is resistant to high ionic strength and can be saturated by increasing the divalent ion or the isoperoxidase concentrations. Treatments in vitro with glucosaminidase or in vivo with tunicamycin show that the carbohydrate part of the isoperoxidase is necessary for the binding. The amino sugar galactosamine inhibits the binding at rather high concentrations. Pharbitis basic isoperoxidase can be bound to zucchini squash microsomes in the presence of Ca²⁺ and conversely.     

Effect of antihistamines and chlorpromazine on the calcium-induced hyperpolarization of the Amphiuma red cell membrane

1. 1. It has previously been demonstrated that an increase in extracellular Ca²⁺ concentration induces a transient increase in K⁺ permeability and associated hyperpolarization of the red cell membrane of the giant salamander, Amphiuma means. This phenomenon is analogous to the Ca²⁺-induced KCl loss observed in ATP-depleted human red cells and red cell ghosts.

2. 2. Histamine, which enhances the Ca²⁺-induced K⁺ loss from depleted human red cells, is without effect on this Ca²⁺-induced hyperpolarization of Amphiuma red cells.

3. 3. Promethazine (10 μM) and mepyramine (1 mM), which inhibit the Ca²⁺-induced K⁺ loss in depleted human red cells, also block the Ca²⁺-related hyperpolarization of Amphiuma erythrocytes.

4. 4. Chlorpromazine (25 μM), despite being a weak antihistamine, is equally effective in blocking the Ca²⁺-induced hyperpolarization of Amphiuma red cells.

5. 5. Ionophore A23187 causes a large and sustained Ca²⁺/K⁺-dependent hyperpolarization even in the presence of normal (1.8 mM) concentrations of Ca²⁺. This hyperpolarization is relatively insensitive to chlorpromazine and promethazine.

6. 6. The inhibition of the Ca²⁺-induced hyperpolarization of the Amphiuma red cell membrane by chlorpromazine and promethazine may be related to their properties as local anaesthetics.

Cytoplasmic changes in level and distribution of glucose-6-phosphatase activities from rat liver during diethylnitrosamine-induced carcinogenesis.

Glucose-6-phosphatase (EC 3.1.3.9) activities were determined in isolated microsomes, cytoplasmic smooth and rough membranes, ribosomes and free cytosol from rat liver undergoing carcinogenesis by diethylnitrosamine (DENA) and compared with cytoplasmic fractions isolated in parallel from healthy animals from the same age.With continuous administration of a low dose of DENA (2.6 mg/kg rat per day for 20 weeks in the drinking water) livers of carcinogen treated rats became heavier than the control livers but the body weight decreased. About 70% of total glucose-6-phosphatase activity could be detected in the microsomal fraction. While there was no significant difference in this activity in both animal groups up to the 4th week, glucose-6-phosphatase of cancerous liver showed a distinct decrease of activity compared with normal liver.During cancer induction this enzyme became more soluble, confirmed by the observation that it was detached from firmer structures of cytoplasm as rough membranes and polysomes and translocated to smooth membranes and the soluble cytoplasmic fraction successively. The corresponding increase in glucose-6-phosphatase activity in the 105 000 g supernatant appears to be due to the loss of enzyme activity in a distinct cytoplasmic membrane fraction. These data strongly suggest that in parallel with alteration of cytoplasmic membrane structures during carcinogen feeding glucose-6-phosphatase is detached from heavier components of the cytoplasm while total activity decreased. Possible mechanisms of these findings are discussed.     

Kinetoplast DNA in the insect trypanosomes Crithidia luciliae and Crithidia fasciculata: II. Sequence evolution of the minicircles

Minicircle sequence evolution has been studied by comparison of the minicircles from Crithidia fasciculata and C. luciliae (C. fasciculata, var. luciliae) by restriction enzyme analysis and hybridization experiments. In contrast to the maxicircle sequence, the minicircle sequence of these trypanosomes evolves very rapidly. No conservation of restriction fragments has been observed and cross-hybridization of minicircles, minicircle fragments, and total kDNA is relatively weak. We conclude that no fragment larger than 550 bp is perfectly conserved between all minicircles of the two trypanosomes. Alterations in the minicircle fragment patterns of our stocks of trypanosomes were even apparent in a cultivation period of 1.5 to 2 years. The alterations suggest a random drift of the sequence which supports a noncodogenic function for the minicircles. Double restriction enzyme digestion experiments show that primary fragments are homogeneous with respect to cleavage by the second enzyme. This suggests that sequence rearrangements, rather than point mutations are the basis of the minicircle sequence heterogeneity.     

Kinetoplast DNA in the insect trypanosomes Crithidia luciliae and Crithidia fasciculata: I. Sequence evolution and transcription of the maxicircle

Kinetoplast DNA from the insect trypanosome Crithidia luciliae contains a maxicircle of 22 × 10⁶ D. We have cleaved this DNA with endonucleases PstI, XbaI, XhoI, SstI, HaeIII, SalII, HindIII, EcoRI, and HapII and constructed a physical map of the 31 cleavage sites. The maxicircle segments hybridizing with total cellular RNA are clustered on one-half of the maxicircle; the genes for the 9 and 12 S mitochondrial (r)RNAs are located on a 1.7-kb segment. Restriction enzyme analysis indicates a sequence homology of more than 96% between the maxicircles of C. luciliae and C. fasciculata, which is not lower than that found between maxicircles of individual Trypanosoma brucei stocks. We conclude therefore that C. luciliae and C. fasciculata are one species and propose to name this species C. fasciculata and to rename C. luciliae as C. fasciculata, var. luciliae. Furthermore we show that the overall maxicircle genome organization of Crithidia resembles that of Trypanosoma.     

Rapid separation of particulate components and soluble cytoplasm of isolated rat-liver cells

A method is described for the rapid separation of mitochondria (plus other particulate components) from the soluble cytoplasm of isolated rat-liver cells. The cells were incubated briefly with a low concentration of digitonin. After rapid centrifugation, the pellet contained more than 90% of the total adenylate kinase and glutamate dehydrogenase activities and the supernatant at least 80% of the lactate dehydrogenase activity. About 60% of total adenine nucleotides in hepatocytes were found in the soluble cytoplasm. The ATP/ADP ratio in the particulate fraction 80 s after exposure to digitonin of hepatocytes metabolizing alanine was 2.0–2.4, and that in the soluble cytoplasm 6–19. In the presence of atractyloside, these values were 3.5–4.4 and 1.3–2.2, respectively.     

Adenine nucleotide translocation in yeast mitochondria. Effect of inhibitors of mitochondrial biogenesis on the ADP translocase

1. Optimal test conditions for adenine nucleotide translocation in Candida utilis mitochondria are a standard medium, consisting of 0.63 M mannitol, 2 mM EDTA (or ethylene glycol tetraacetic acid, EGTA), 10 mM morpholinopropane sulfonic acid (pH 6.8), and a temperature of 0 °C.

2. Adenine nucleotide translocation in C. utilis mitochondria is an exchange-diffusion process. The whole pool of internal adenine nucleotides is exchangeable, ADP being the most readily exchangeable nucleotide. The rate of mitochondrial ADP exchange, but not the K_m value, depends on growth conditions. At 0 °C, the rate is about 3 to 4 nmoles ADP/min per mg protein for mitochondria obtained from yeast grown in the presence of 1.5% glucose; it rises to 11.5 nmoles when glucose is replaced by 3% ethanol in the growth medium. The K_m value for ADP is 2 μM. The Q₁₀ is about 2 between 0 and 20 °C. Among other exchangeable adenine nucleotides are ATP, dADP and the methylene and the hypophosphate analogues of ADP. Unlike mammalian mitochondria, C. utilis mitochondria are able to transport external UDP by a carboxyatractyloside-sensitive process.

3. Under conditions of oxidative phosphorylation (phosphate and substrate present in an aerated medium), added ADP is exchanged with internal ATP. A higher ATP/ADP ratio was found in the extramitochondrial space than in the intramito-chondrial space. The difference between the calculated phosphate potentials in the two spaces was 0.9–1.7 kcal/mole.

4. Atractyloside, carboxyatractyloside, bongkrekic acid and palmityl-CoA inhibit mitochondrial adenine nucleotide translocation in C. utilis as they do in mammalian mitochondria, but 2 to 4 times less efficiently. The inhibition due to atractyloside or palmityl-CoA is competitive with respect to ADP whereas that due to bongkrekic acid and carboxyatractyloside is non-competitive. Carboxyatractyloside and atractyloside inhibitions are additive. The apparent K_d for the binding of [³⁵S]-carboxyatractyloside and [¹⁴C]bongkrekic acid is 10–15 nM and the concentration of sites 0.4–0.6 nmole/mg protein in both cases. [³⁵S]Carboxyatractyloside binding is competitively displaced by atractyloside and vice versa.

5. Binding of [¹⁴C]ADP has been carried out with mitochondria depleted of their endogenous adenine nucleotides by incubation with phosphate and Mg²⁺ at 20 °C. The amount of bound [¹⁴C]ADP which is atractyloside removable is 0.08–0.16 nmole/mg protein.

6. The rate of ADP transport is quite different in mitochondria isolated from C. utilis, according to whether it is grown on glucose, or on ethanol or in the presence of chloramphenicol; for instance, it decreases by 10 times when 3% ethanol in the growth medium is replaced by 10% glucose and by 5 times when chloramphenicol is added to the medium. These variations are accompanied by parallel variations in cytochrome aa₃. The number of atractyloside-sensitive ADP binding sites is not modified by the above conditions of culture, nor the number of [³⁵S]carboxyatractyloside binding sites. The affinity for ADP is apparently not significantly modified, nor the size of the endogenous adenine nucleotide pool. In contrast to glucose repression or chloramphenicol inhibition, semi-anaerobiosis in C. utilis lowers significantly the mitochondrial binding capacity for carboxyatractyloside. Strict anaerobiosis in S. cerevisiae results in a practical loss of the cytochrome oxidase activity, and also of the carboxyatractyloside and ADP binding capacity. Transition from anaerobiosis to aerobiosis restores the cytochrome oxidase activity and the ADP and carboxyatractyloside binding capacities.