Preparation and Properties of Sweet Potato Mitochondria

Functional molecular aspects of the NADH dehydrogenases of plant mitochondria

There are multiple routes of NAD(P)H oxidation associated with the inner membrane of plant mitochondria. These are the phosphorylating NADH dehydrogenase, otherwise known as Complex I, and at least four other nonphosphorylating NAD(P)H dehydrogenases. Complex I has been isolated from beetroot, broad bean, and potato mitochondria. It has at least 32 polypeptides associated with it, contains FMN as its prosthetic group, and the purified enzyme is sensitive to inhibition by rotenone. In terms of subunit complexity it appears similar to the mammalian and fungal enzymes. Some polypeptides display antigenic similarity to subunits from Neurospora crassa but little cross-reactivity to antisera raised against some beef heart complex I subunits. Plant complex I contains eight mitochondrial encoded subunits with the remainder being nuclear-encoded. Two of these mitochondrial-encoded subunits, nad7 and nad9, show homology to corresponding nuclear-encoded subunits in Neurospora crassa (49 and 30 kDa, respectively) and beef heart CI (49 and 31 kDa, respectively), suggesting a marked difference between the assembly of CI from plants and the fungal and mammalian enzymes. As well as complex I, plant mitochondria contain several type-II NAD(P)H dehydrogenases which mediate rotenone-insensitive oxidation of cytosolic and matrix NADH. We have isolated three of these dehydrogenases from beetroot mitochondria which are similar to enzymes isolated from potato mitochondria. Two of these enzymes are single polypeptides (32 and 55 kDa) and appear similar to those found in maize mitochondria, which have been localized to the outside of the inner membrane. The third enzyme appears to be a dimer comprised of two identical 43-kDa subunits. It is this enzyme that we believe contributes to rotenone-insensitive oxidation of matrix NADH. In addition to this type-II dehydrogenases, several observations suggest the presence of a smaller form of CI present in plant mitochondria which is insensitive to rotenone inhibition. We propose that this represents the peripheral arm of CI in plant mitochondria and may participate in nonphosphorylating matrix NADH oxidation.

Subcellular distribution of selenium during uptake and its influence on mitochondrial oxidations in germinating Vigna radiata L

The metabolic significance of Se in plants is not well documented, though the presence of many selenoenzymes in bacteria and the essentiality of Se in higher animals is established. Since germination is an active process in plant growth and metabolism, the effect of Se was investigated in germinating Vigna radiata L, a nonaccumulating Se-deficient legume. Growth and protein were enhanced in seedlings supplemented with selenium (Se) as sodium selenite in the medium up to 1 microgram/mL. The pattern of uptake of 75Se in the differentiating tissues and the subcellular distribution were investigated. The percentage of incorporation of 75Se was greater in the mitochondria at the lowest level (0.5 micrograms/mL) of Se supplementation compared to higher levels of Se exposure. Proteins precipitated from the postmitochondrial supernatant fractions, when separated by means of polyacrylamide gel electrophoresis (PAGE), indicated a major selenoprotein in the seedlings germinated at 2.0 micrograms/mL Se. In seedlings grown with supplemented Se, enhanced respiratory control ratio and succinate dehydrogenase activity were observed in the mitochondria of tissues, indicative of a role for Se in mitochondrial membrane functions.

Energetics of proline transport in corn mitochondria

The mechanism of proline entry into the matrix region of isolated corn mitochondria (Zea mays L. Mo17 x B73) was investigated by measuring osmotically induced changes of mitochondrial size (changes in A(520)) in combination with oxygen uptake measurements. Using NADH oxidation to generate the electrochemical gradient, we have determined that proline transport is stereospecific and that it can be inhibited by the proline analog l-thiazolidine-4-carboxylic acid.The energetics of proline transport was investigated by measuring the effects of FCCP (p-trifluoromethoxycarbonyl cyanide phenylhydrazone) and valinomycin on mitochondrial swelling and substrate oxidation. Proline transport and resulting oxidation were found to be partially dependent upon the energy of the electrochemical gradient. At low proline concentrations, entry was found to be primarily independent of the gradient (based on insensitivity to FCCP), whereas at higher proline concentrations a gradient-dependent mechanism became involved. Results with valinomycin indicated that proline transport and oxidation are dependent upon the pH potential across the membrane rather than the electrical (membrane) potential.

Evidence for the role of malic enzyme in the rapid oxidation of malate by cod heart mitochondria

Mitochondria isolated from the heart of cod (Gadus morrhua callarias) oxidized malate as the only exogenous substrate very rapidly. Pyruvate only slightly increased malate oxidation by these mitochondria. This is in contrast with the mitochondria isolated from rat and rabbit heart which oxidized malate very slowly unless pyruvate was added. Arsenite and hydroxymalonate (an inhibitor of malic enzyme) inhibited the respiration rate of mitochondria isolated from cod heart, when malate was the only exogenous substrate. Inhibition caused by hydroxymalonate was reversed by the addition of pyruvate. In the presence of arsenite, malate was converted to pyruvate by cod heart mitochondria. Cod heart mitochondria incubated in the medium containing Triton X-100 catalyzed the reduction of NADP+ in the presence of L-malate and Mn2+ at relatively high rate (about 160 nmoles NADPH formed/min/mg mitochondrial protein). The oxidative decarboxylation of malate was also taking place when NADP+ was replaced by NAD+ (about 25 nmol NADH formed per min per mg mitochondrial protein). These results suggest that the mitochondria contain both NAD+- and NADP+-linked malic enzymes. These two activities were eluted from DEAE-Sephacel as two independent peaks. It is concluded that malic enzyme activity (presumably both NAD+- and NADP+-linked) is responsible for the rapid oxidation of malate (as the only external substrate) by cod heart mitochondria.

Effect of NAD on Malate Oxidation in Intact Plant Mitochondria

Potato tuber mitochondria oxidizing malate respond to NAD(+) addition with increased oxidation rates, whereas mung bean hypocotyl mitochondria do not. This is traced to a low endogenous content of NAD(+) in potato mitochondria, which prove to take up added NAD(+). This mechanism concentrates NAD(+) in the matrix space. Analyses for oxaloacetate and pyruvate (with pyruvate dehydrogenase blocked) are consistent with regulation of malate oxidation by the internal NAD(+)/NADH ratio.

Effect of bicarbonate and oxaloacetate on malate oxidation by spinach leaf mitochondria

Mitochondria isolated from spinach leaves oxidized malate by both a NAD+-linked malic enzyme and malate dehydrogenase. In the presence of sodium arsenite the accumuation of oxaloacetate and pyruvate during malate oxidation was strongly dependent on the malate concentration, the pH in the reaction medium and the metabolic state condition. Bicarbonate, especially at alkaline pH, inhibited the decarboxylation of malate by the NAD+-linked malic enzyme in vitro and in vivo. Analysis of the reaction products showed that with 15 mM bicarbonate, spinach leaf mitochondria excreted almost exclusively oxaloacetate. The inhibition by oxaloacetate of malate oxidation by spinach leaf mitochondria was strongly dependent on malate concentration, the pH in the reaction medium and on the metabolic state condition. The data were interpreted as indicating that: (a) the concentration of oxaloacetate on both sides of the inner mitochondrial membrane governed the efflux and influx of oxaloacetate; (b) the NAD+/NADH ratio played an important role in regulating malate oxidation in plant mitochondria; (c) both enzymes (malate dehydrogenase and NAD+-linked malic enzyme) were competing at the level of the pyridine nucleotide pool, and (d) the NAD+-linked malic enzyme provided NADH for the reversal of the reaction catalyzed by the malate dehydrogenase.

Photosynthesis in the Higher Plant Vicia faba: V. Role of Malate as a Precursor of the Tricarboxylic Acid Cycle

In the higher plant Vicia faba, anomalous labeling patterns in the organic acids and related amino acids of the tricarboxylic acid cycle which result from photosynthetic (14)CO(2) fixation (in conjunction with an enzyme localization pattern unique to plant mitochondria) suggest that the tricarboxylic acid cycle functions primarily as a pathway leading to glutamic acid biosynthesis during autotrophic growth. The distribution of isotope in citrate indicates little recycling of oxaloacetate for the resynthesis of citrate. Rather, malate appears to provide both the C(2) and C(4) fragments for the synthesis of citrate, and [(3)H]formate and (14)CO(2)-labeling patterns implicate serine as the ultimate C(3) precursor of malate.

In Vitro Study of Mitochondrial Protein Synthesis during Mitochondrial Biogenesis in Excised Plant Storage Tissue

Mitochondrial biogenesis was induced in Jerusalem artichoke (Helianthus tuberosus) tuber by aging tissue discs in distilled water for up to 26 hours. Changes in the purified mitochondrial fraction during aging included an increase in both protein content and specific respiratory activity. Using intact isolated mitochondria, conditions were optimized for incorporation of radioactive amino acid into protein. Incorporation was dependent upon the supply of an oxidizable substrate or an external ATP-generating system and showed characteristic sensitivity to inhibitors of protein synthesis. Aging of the tissue resulted in a 3-fold increase in the rate of in vitro incorporation of [(35)S]methionine into mitochondrial protein. An analysis of the free amino acid pool in the mitochondrial fraction showed that the decrease in methionine level during aging of intact tissue was sufficient to account for the increased rate of protein labeling. The activation of mitochondrial biogenesis which occurs after slicing is not dependent on an increase in the capacity of mitochondria to synthesize protein as assayed in vitro.Analysis, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography, showed that isolated mitochondria synthesized about 15 polypeptides in the molecular weight range 8,000 to 55,000. As aging proceeded, significant changes were observed in the relative rates of labeling of three out of the eight major polypeptides synthesized by mitochondria in vitro.

Effect of Ethylene and Oxygen on the Development of Cyanide-resistant Respiration in Whole Plant Mitochondria

Mitochondria from whole potatoes (Solanum tuberosum) ordinarily fail to oxidize respiratory substrates and to consume molecular O(2) in the presence of cyanide. Mitochondrial preparations obtained from tubers previously held for 24 hours in ethylene (10 microliters per liter) in air are only partially inhibited by cyanide. Application of ethylene in 100% O(2) led to an additional increase in the resistance of the mitochondrial respiration to cyanide. The resistance to cyanide was accompanied by a decrease in the respiratory control but no change in oxidative phosphorylation as shown by the measurement of ATP synthesis.The development of resistance to cyanide following the application of ethylene appears to require whole tubers and may represent an inductive process.

Regulation of malate oxidation in isolated mung bean mitochondria: I. Effects of oxaloacetate, pyruvate, and thiamine pyrophosphate

In order to investigate the relationship between malate oxidation and subsequent cycle reactions, the effects of oxaloacetate, pyruvate, and thiamine pyrophosphate on malate oxidation in mung bean (Phaseolus aureus var. Jumbo) hypocotyl mitochondria were quantitatively examined. Malate oxidation was optimally stimulated by addition of pyruvate and thiamine pyrophosphate, whose addition lowered the apparent Km for malate from 5 mm to 0.1 mm. Intermediate analysis showed that the stimulatory effect was correlated with removal of oxaloacetate to citrate. Oxaloacetate added alone was shown not to be metabolized until addition of pyruvate and thiamine pyrophosphate; then oxaloacetate was converted in part to pyruvate and also to citrate. These results establish that malate oxidation in mung bean mitochondria is subject to control by oxaloacetate levels, which are primarily determined by the resultant of the activities of malate dehydrogenase, citrate synthase, and pyruvate dehydrogenase.

Control of Changes in Mitochondrial Activities during Aging of Potato Slices

Aging of slices of potato tuber (Solanum tuberosum L.) in an aerated liquid medium induces a number of changes in mitochondrial activities. A nonphosphorylative, cyanide-insensitive electron transport pathway (alternate pathway) is brought into operation. The rate of oxidation of exogenous NADH increases markedly and the efficiency of phosphorylation with this substrate remains the same as it is in mitochondria isolated from fresh tissue slices. On the contrary, the rates of oxidation of succinate and malate do not increase while lower phosphorylative efficiencies indicate that a fraction of their electrons reaches oxygen through the alternate pathway. Chloramphenicol, a specific inhibitor of the mitochondrial protein-synthesizing system, has no effect whatsoever on these events. However, cycloheximide, which acts on the corresponding cytoplasmic system, prevents both the development of the alternate pathway and the rise in the rate of oxidation of exogenous NADH. These effects are interpreted as showing a specific control of the cytoplasmic protein-synthesizing system on the changes in mitochondrial oxidations during aging.

The activation of non-phosphorylating electron transport by adenine nucleotides in Jerusalem-artichoke (Helianthus tuberosus) mitochondria

In isolated plant mitochondria the oxidation of both succinate and exogenous NADH responded in the expected manner to the addition of ADP or uncoupling agents, and the uncoupled rate of respiration was often in excess of the rate obtained in the presence of ADP. However, the oxidation of NAD+-linked substrates responded in a much more complex manner to the addition of ADP or uncoupling agents such as carbonyl cyanide p-trifluoromethoxyphenylhydrazone to mitochondria oxidizing pyruvate plus malate failed to result in a reliable stimulation; this uncoupled rate could be stimulated by adding AMP or ADP in the presence of oligomycin or bongkrekic acid. Spectrophometric measurements showed that the addition of AMP or ADP resulted in the simultaneous oxidation of endogenous nicotinamide nucleotide and the reduction of cytochrome b. ADP was only effective in bringing about these changes in redox state in the presence of Mg2+ whereas AMP did not require Mg2+. It was concluded that AMP activated the flow of electrons from endogenous nicotinamide nucleotide to cytochrome b, possible at the level of the internal NADH dehydrogenase.

Cyanide-resistant Respiration of Sweet Potato Mitochondria

The oxidation of malate and succinate by sweet potato mitochondria (Ipomoea batatas [L.] Lam.) was blocked only partly by inhibitors of complexes III (2-heptyl-4-hydroxyquinoline-N-oxide) and IV (cyanide and azide). The respiration insensitive to inhibitors of complexes III and IV was inhibited by salicylhydroxamic acid. Essentially complete inhibition was obtained with inhibitors of complex I (rotenone, amytal, and thenoyltrifluoroacetone) and complex II (thenoyltrifluoroacetone). The observations indicated that electrons were transferred to the cyanide-resistant pathway from ubiquinone or from nonheme iron (iron-sulfur) proteins of complexes I and II before reaching the b cytochromes. In contrast, the oxidation of exogenous NADH did not involve the alternate pathway, as indicated by complete inhibition by inhibitors of complexes III and IV and the absence of an effect of inhibitors of complexes I and II. Hence, electrons from exogenous NADH appear to pass directly to complex III in sweet potato mitochondria.

The effect of nucleotides and inhibitors on respiration in isolated wheat mitochondria

The effect of mono-, di-, and trinucleoside phosphates and respiratory inhibitors on respiration in winter wheat (Triticum aestivum L. cv. Rideau) mitochondria has been examined. When added during state 4 respiration, subsequent to addition of ADP, all of the dinucleotides stimulated oxidation and induced respiratory control with all substrates examined. Similar results were obtained with AMP, but other mononucleotides and all trinucleotides did not affect the rate of oxidation. Nucleoside diphosphates did not stimulate respiration when added prior to the addition of ADP, but subsequent addition of AMP, ADP, or ATP re-established coupled respiration in the presence of the dinucleotides.The duration of 2, 4-dinitrophenol stimulated respiration during oxidation of alpha-ketoglutarate was found to be dependent on the amount of AMP, ADP, or ATP added, either prior, or subsequent to, addition of the uncoupler. The addition of oligomycin during 2, 4-dinitrophenol stimulated respiration reestablished coupled respiration with low ADP/O ratios, when added after addition of ATP or conditions which allow formation of ATP from added ADP. The nucleoside diphosphates, other than ADP, did not stimulate oxidation of alpha-ketoglutarate in the presence of 2, 4-dinitrophenol until a small amount of adenine nucleotide was added to the system. The results suggest that dinucleotides other than ADP, are able to participate in the energy conversion processs of the mitochondria, probably via transphosphorylation reactions.

The control of NAD specific malic enzyme from cauliflower bud mitochondria by metabolites

NAD malic enzyme (EC. 1.1.1.39) has been purified from cauliflower (Brassica oleracea. var. botrytis) bud mitochondria. The enzyme exhibits complex regulatory properties being activated by a variety of metabolites including glycolytic intermediates, CoA, sulphate and Krebs cycle acids-the tricarboxylic acids with the exception of citrate being more effective than dicarboxylic acids. Fructose diphosphate which is a positive effector of the enzyme increases the affinity of the enzyme for L-malate.The enzyme is inhibited by glutamate, aspartate, phosphate and ATP, in the latter case the inhibition is largely due to chelation of Mg(2+). The plot of rate versus malate concentration is sigmoid at pH 7.0 with Mg(2+) but normal Michaelis-Menten kinetics are observed with Mn(2+). The molecular weight of the enzyme as measured by gel filtration is ca. 400000. The physiological significance of the responses to metabolites is discussed.

The Effect of Exogenous Nicotinamide Adenine Dinucleotide on the Oxidation of Nicotinamide Adenine Dinucleotide-linked Substrates by Isolated Plant Mitochondria

The oxidation of malate, citrate, and alpha-ketoglutarate by cauliflower (Brassica oleacea L.) bud mitochondria was inhibited by rotenone. This inhibition was relieved upon addition of NAD(+) to the medium, and ADP/O values were lowered to less than 2 when both rotenone and NAD(+) were present. Dinitrophenol did not affect the relief of rotenone inhibition by exogenous NAD(+).

The Metabolism of Oat Leaves during Senescence: I. Respiration, Carbohydrate Metabolism, and the Action of Cytokinins

When the detached first leaves of green or etiolated oat (Avena sativa cv. Victory) seedlings senesce in the dark, their oxygen consumption shows a large increase, beginning after 24 hours and reaching a peak of up to 2.5 times the initial rate by the 3rd day. This effect takes place while the chlorophyll of green leaves, or the carotenoid of etiolated leaves, is steadily decreasing. Kinetin, at a concentration which inhibits the decrease in pigment, completely prevents the respiratory rise; instead, the oxygen consumption drifts downwards. Lower kinetin concentrations have a proportional effect, 50% reduction of respiration being given by about 0.1 mg/l. About one-fifth of the respiratory rise may be attributed to the free amino acids which are liberated during senescence; several amino acids are shown to cause increases of almost 50% in the oxygen consumption when supplied at the concentrations of total amino acid present during senescence. A smaller part of the rise may also be due to soluble sugars liberated during senescence, largely coming from the hydrolysis of a presumptive fructosan. The remainder, and the largest part, of the increase is ascribed to a natural uncoupling of respiration from phosphorylation. This is deduced from the fact that dinitrophenol causes a similar large rise in the oxygen consumption of the fresh leaves or of leaf segments kept green with kinetin, but causes only a very small rise when the oxygen consumption is near its peak in senescent controls. The respiration of these leaves is resistant to cyanide, and 10 mm KCN even increases it by some 30%; in contrast, etiolated leaves of the same age, which undergo a similar rise in oxygen consumption over the same time period, show normal sensitivity to cyanide. The respiratory quotient during senescence goes down as low as 0.7, both with and without kinetin, though it is somewhat increased by supplying sugars or amino acids; glucose or alanine at 0.3 m bring it up to 1.0 and 0.87, respectively.N(6)-Benzylaminopurine and Delta-2-isopentenylaminopurine act similarly to kinetin in repressing the respiratory rise, the former being five times as active as kinetin, while the latter has only 1% of the activity of kinetin. Zeatin also powerfully prevents senescence. Because the repression of the respiratory rise is shown by each cytokinin at the concentration at which it inhibits senescence, the action is ascribed in both cases to the maintenance of a tight coupling between respiration and phosphorylation. It is pointed out that such an effect would explain many features of cytokinin action.A change in the methodology of the senescence experiments is described and compared with the method previously used, and the influence of temperature and age of the plants on the course of leaf senescence are presented in detail.

The influence of osmolarity on the reduction of exogenous cytochrome c and permeability of the inner membrane of Jerusalem artichoke mitochondria

The stimulation of succinate-cytochrome c reductase in Jerusalem artichoke mitochondria by lowering osmolarity was found to be associated with conformational changes in the inner membrane rather than with rupture of the outer membrane. This conclusion is based on the following evidence. (1) When the activation of succinate dehydrogenase was measured by using either K(3)Fe(CN)(6) or exogenous cytochrome c as an electron acceptor, electron flow to cytochrome c was always 7% of that to K(3)Fe(CN)(6) throughout the activation process. (2) The rate of exogenous cytochrome c reduction by succinate and NADH was directly related to the maximum rate of electron flow as determined by oxygen utilization. These two observations are not consistent with the low rate of succinate-cytochrome c reductase being limited by a permeability barrier at the outer membrane. (3) In addition to stimulating the succinate-cytochrome c reductase, lowering the osmolarity caused simultaneous changes in the permeability of the inner membrane to ferricyanide and NADH. The data show that lowering the osmolarity results in progressive changes in the permeability of the inner membrane. The first change detected was an increased permeability to K(3)Fe(CN)(6), then a simultaneous increase in accessibility of the respiratory chain to exogenous cytochrome c and an increased permeability to NADH, followed finally by rupture as measured by the release of malate dehydrogenase.

[Inhibition of respiratory enzymes in mitochondria of green leaves]

1. Of the buffer substances introduced by Good, only N-2-hydroxy-ethylpiperazine-N-2-ethanesulfonic acid (HEPES) and N-tris(hydroxymethyl)-methyl-2-aminoethanesulfonic acid (TES) were found suitable for the isolation of mitochondria by means of density gradient centrifugation in a silica sol. Addition of 1% polyvinylpyrrolidone remarkably reduced the respiration rate and diminished the respiratory control, whereas 2% dextran improved the rates. 2. Fifty mM malonate inhibited succinate oxidation by 55-72% compared with the controls; in addition an uncoupling effect was observed. Similar results were obtained with 2.5 mM amytal. 3. Antimycin A, in contrast, did not affect the respiratory control, while the respiration rate was depressed to 55% of that in the control. 4. Azide (20 mM) had only a slight effect on the two parameters of leaf mitochondria. 5. It can be concluded that mitochondria of leaf cells are provided with the same respiratory enzymes as those of other plant materials.

Ion transport induced by polycations and its relationship to loose coupling of corn mitochondria

Treatment of corn mitochondria (Zea mays L., WF9 (Tms) x M14) with polycations (protamine, pancreatic ribonuclease, or polylysine) releases acceptorless respiration if phosphate is present. Concurrently, there is extensive active swelling which is reversed when respiration is uncoupled or stopped. Mersalyl, the phosphate transport inhibitor, blocks both the release of respiration and the active swelling. Diversion of energy into phosphate transport lowers respiratory control and ADP: O ratios. This response is termed "loose coupling" in distinction to "uncoupling" in which energy is made unavailable for either transport or ATP formation. Corn mitochondria as used here are endogenously loose coupled to some extent, and show state 4 respiration linked to active transport.The action of polycations can be partially mimicked by lowering pH of the suspending medium; both give swelling in sucrose medium and increased light absorbancy. Triton X-100, a nonionic detergent, will uncouple and accentuate active swelling, but unlike polycations it will not release state 4 respiration. Calcium ion acts something like polycation in activating phosphate transport and releasing respiration, and polycation appears to block entry of Ca(2+).It is speculated that neutralization of certain negatively charged acid groups on the membranes by polycations increases permeability to solutes and decreases coulombic repulsion of phosphate in approaching transport sites. In consequence, respiration rates and active transport rates increase.

Cyanide-insensitive Respiration in Plant Mitochondria

Pathways of electron transport have been studied in mitochondria isolated from hypocotyls of etiolated mung bean seedlings and skunk cabbage spadices that show cyanide-resistant respiratory activity. The residual flux through cytochrome c oxidase is shown to be small in comparison with the flux through an unidentified alternative oxidase that is known to have a high affinity for oxygen. This alternative oxidase is not a cytochrome. Skunk cabbage and mung bean mitochondria contain cytochromes a and a(3) that have absorption peaks differing slightly from those of animal preparations. A slow oxidation-reduction of cytochrome a(3)-CN has been demonstrated. Cytochromes b undergo oxidation and reduction in the presence of cyanide but play no essential role in the cyanide-resistant pathway. Antimycin inhibits to an extent similar to that of cyanide; the respiratory chain bifurcates on the substrate side of the antimycin-sensitive site. Evidence is presented for the selective inhibition by thiocyanate, alpha, alpha'-dipyridyl, and 8-hydroxyquinoline of the alternative oxidase pathway, which may therefore contain a non-heme iron protein.

A Lack of Specificity for Ethylene-induced Mitochondrial Changes

A critical evaluation was made of the hypothesis that the primary mode of action of ethylene in inducing physiological responses is by changing the permeability of cell organelles. The parameter investigated was the evaluation of the influence of ethylene and other gases on mitochondrial oxidation and swelling. Spectrometric evidence demonstrated that mitochondria prepared with good respiratory control can be induced to swell more rapidly with ethylene and other aliphatic gases (ethane, propene, propane, I-butene) in test solutions of 0.125 m KCl. The fact that saturated as well as unsaturated hydrocarbon gases elicited similar changes provides evidence that ethylene does not directly alter membrane permeability as its mechanism of action.

Necessary conditions for isolation of tightly coupled higher plant mitochondria

A number of parameters associated with the isolation of plant mitochondria were carefully examined in the hope of optimizing the isolation technique. Dark-grown mung bean (Phaseolus aureus var. Jumbo) hypocotyls were used as the source of mitochondria. Necessary conditions for the isolation of tightly coupled plant mitochondria include: (a) gentle tissue disruption; (b) rigorous exclusion of contaminating particles from the mitochondrial fraction; (c) the use of an optimal grinding medium containing a high concentration of mannitol, 10 mm phosphate or triethanolamine buffer to maintain the pH above 7.2, ethylenediaminetetraacetic acid at 1 mm level, cysteine at a low concentration (0-5 mm), and a high concentration of bovine serum albumin (0.1-1.0%); and (d) the use of the proper wash and suspending medium consisting of mannitol, buffer, and bovine serum albumin at the same concentration as in the grinding medium.

Oxidative activity of mitochondria isolated from plant tissues sensitive and resistant to chilling injury

Arrhenius plots of the respiration rates of mitochondria isolated from chilling sensitive plant tissues (tomato and cucumber fruit, and sweet potato roots) showed a linear decrease from 25 C to about 9 to 12 C (with Q(10) values of 1.3 to 1.6), at which point there was a marked deviation with an increased slope as temperatures were reduced to 1.5 C (Q(10) of 2.2 to 6.3). The log of the respiration rate of mitochondria from chilling resistant tissues (cauliflower buds, potato tubers, and beet roots) showed a linear decrease over the entire temperature range from 25 to 1.5 C with Q(10) values of 1.7 to 1.8. Phosphorylative efficiency of mitochondria from all the tissues, as measured by ADP:O and respiratory control ratios, was not influenced by temperatures from 25 to 1.5 C. These results indicate that an immediate response of sensitive plant tissues to temperatures in the chilling range (0 to 10 C) is to depress mitochondrial respiration to an extent greater than that predicted from Q(10) values measured above 10 C. The results are also consistent with the hypothesis that a phase change occurs in the mitochondrial membrane as the result of a physical effect of temperature on some membrane component such as membrane lipids.

The effect of respiratory inhibitors on NADH, succinate and malate oxidation in corn mitochondria

The effect of a series of respiratory inhibitors on the oxidation of NADH in state 4 and state 3 conditions was studied with corn shoot mitochondria. Comparisons were made using malate and succinate as substrates. The inhibitors, rotenone, amytal, antimycin A and cyanide, inhibited oxidation of NADH in state 3 but rotenone and amytal did not inhibit oxidation in state 4. The inhibition by antimycin A was partially overcome by the presence of cytochrome c. The results indicate the presence of alternative pathways available for NADH oxidation depending on the metabolic condition of the mitochondria. Under state 4 conditions, NADH oxidation bypasses the amytal and rotenone sensitive sites but under state 3 conditions a component of the NADH respiration appears to be oxidized by an internal pathway which is sensitive to these inhibitors. Still a third pathway for NADH oxidation is dependent on the addition of cytochrome c and is insensitive to antimycin A. Succinate oxidation was sensitive to cyanide and antimycin A under both state 4 and state 3 conditions as well as amytal and rotenone under state 3 conditions but was not inhibited by amytal and rotenone under state 4 conditions. Malate oxidation was inhibited by cyanide, rotenone and amytal under both state 4 and state 3 conditions. Antimycin A inhibited state 3 but did not appreciably alter state 4 rates of malate oxidation. With all substrates tested inhibition by antimycin A was greatly facilitated by preswelling the mitochondria for 10 min. This was interpreted to indicate that swelling increases the accessibility of antimycin A to the site of inhibition.

Effects of 3,5-Dihalogenated-4-hydroxybenzonitriles on the Activity of Mitochondria From White Potato Tubers

Effects of the herbicide 3,5-diiodo-4-hydroxybenzonitrile (ioxynil), and its dibromo and dichloro analogs, upon the respiration of mitochondria isolated from white potato tubers (Solanum tuberosum L.) were investigated. Mitochondrial-mediated oxygen uptake was monitored polarographically with a platinum oxygen electrode.With succinate as substrate for mitochondrial oxidation, ioxynil stimulated both ADP-limited and ADP + phosphate-deficient oxygen utilization. Ioxynil also circumvented oligomycin-inhibited respiration and slightly stimulated mitochondrial ATPase activity. Responses produced by ioxynil on respiration were similar to, but occurred at lower concentrations than, those of 2,4-dinitrophenol.The dibromo- and dichloro-substituted analogs of ioxynil also stimulated ADP-limited respiration and released oligomycin-inhibited oxygen uptake. Based on concentration, the decreasing order of uncoupling activity was I > Br > Cl with respect to the halogen substituents.

Studies on ultrastructure and purification of isolated plant mitochondria

Sweetpotato mitochondria, that showed respiratory control, were studied with respect to ultrastructure. If fixed in media containing sucrose at 0.4 M, the cristae were dilated and the matrix was highly condensed. A more orthodox ultrastructural form was observed when the mitochondria were fixed in a medium containing sucrose at 0.25 M, i.e., the matrix was more expanded, the cristae were less dilated, and peripherally, the inner membrane element lay adjacent to the outer membrane element. These results are discussed in terms of a sucrose-accessible space (space between outer and inner membrane elements including intracristal space), and a space relatively inaccessible to sucrose (matrix). Ultrastructural shifts were not observed with change in metabolic steady state of the mitochondria. High resolution electron micrographs showed that the ultrastructure of sweetpotato mitochondria is very similar to that of animal mitochondria.Purity and homogeneity of mitochondrial fractions were followed both by phase-contrast and electron microscopy. Preparations from sweetpotato, using older methods, were relatively homogeneous with respect to particle type and size, whereas avocado preparations contained a high proportion of chloroplasts and cellular debris. A method of purification involving sucrose-density-gradient centrifugation was developed. Purified mitochondria exhibited respiratory control and appeared similar to unpurified mitochondria under the electron microscope.

Respiratory components of Aspergillus niger mitochondria

The respiratory components of tightly coupled mitochondria from the filamentous fungus Aspergillus niger were studied. Cytochromes a + a(3), b, and c + c(1) were identified by difference spectra. The cytochrome spectra were qualitatively similar to yeast and rat liver mitochondria. The mitochondria contained, per gram of protein, an average of 2.9 and 7.0 mumoles of ubiquinone and nicotinamide adenine dinucleotide, respectively.

Photosynthetic control by isolated pea chloroplasts

Isolated pea chloroplasts undergo both cyclic and non-cyclic electron flow. Both processes are coupled to photophosphorylation. During non-cyclic flow the rate of oxygen production showed ADP-governed ;photosynthetic control' analogous to respiratory control of isolated mitochondria. Measurements of ADP/O and photosynthetic control ratios yielded values of 1-1.3 and 2-5.7 respectively. ;Photosynthetic control' was shown to be dependent on the intactness of the chloroplasts.

On methods of isolation of active, tightly coupled mitochondria of wheat seedlings

Tightly coupled mitochondria can be isolated from wheat seedlings 1) if young seedlings are used, 2) if the grinding medium is buffered and contains bovine serum albumin (BSA), 3) if the isolation procedure, including centrifugation is 10 to 11 minutes long. Mitochondria isolated in this manner oxidize alpha-ketoglutarate, malate and NADH. Respiratory control (R.C.) values are around 6, 3, and 10, respectively. ADP:O values with those substrates are 4.0, 2.9, and 1.7, respectively. Mitochondria are stable for 3 hours. It is suggested that the technique may be used for preparation of mitochondria for comparative studies since activities of these mitochondria are highly reproducible.

Intermediate reactions of oxidative phosphorylation in mitochondria from cabbage

Respiratory control ratios between 2.0 and 9.0 were obtained by comparison of the respiratory rates of cabbage mitochondria in the presence and in the absence of individual components of the system used to provide ADP and by comparing the rates before and after exhaustion of added ADP. These results indicate that respiration in cabbage mitochondria is controlled by the availability of ADP, which serves as the phosphate acceptor. Pentachlorophenol (PCP), 2,4-dinitrophenol (DNP), gramicidin and oleic acid inhibited phosphorylation to a greater extent than respiration in the cabbage mitochondria, but these reagents did not stimulate respiration in the absence of a phosphate acceptor. Respiration was stimulated by DNP only in the presence of added ATP.2,4-Dinitrophenol, pentachlorophenol, dicumarol and gramicidin did not stimulate ATPase activity either in the presence or absence of added Mg(2+). Oleic acid stimulated ATPase activity in the presence of added Mg(2+), but did not stimulate respiration even in the presence of added ATP. The ATP-(32)Pi exchange rate was increased many fold in the presence of added Mg(2+). Oleic acid and 2,4-dinitrophenol inhibited the exchange almost completely.