PubMed Health⌕ Search

Biomedical subjects

W D Bonner

Publications and source records attributed to W D Bonner.

At least 55 records · Page 3Linked to original sources
PubMed1971

Specific inhibition of the cyanide-insensitive respiratory pathway in plant mitochondria by hydroxamic acids.

Hydroxamic acids, R-CONHOH, are inhibitors specific to the respiratory pathway through the alternate, cyanide-insensitive terminal oxidase of plant mitochondria. The nature of the R group in these compounds affects the concentration at which the hydroxamic acids are effective, but it appears that all hydroxamic acids inhibit if high enough concentrations are used. The benzhydroxamic acids are effective at relatively low concentrations; of these, the most effective are m-chlorobenzhydroxamic acid and m-iodobenzhydroxamic acid. The concentrations required for half-maximal inhibition of the alternate oxidase pathway in mung bean (Phaseolus aureus) mitochondria are 0.03 mm for m-chlorobenzhydroxamic acid and 0.02 mm for m-iodobenzhydroxamic acid. With skunk cabbage (Symplocarpus foetidus) mitochondria, the required concentrations are 0.16 for m-chlorobenzhydroxamic acid and 0.05 for m-iodobenzhydroxamic acid. At concentrations which inhibit completely the alternate oxidase pathway, these two compounds have no discernible effect on either the respiratory pathway through cytochrome oxidase, or on the energy coupling reactions of these mitochondria. These inhibitors make it possible to isolate the two respiratory pathways and study their mode of action separately. These inhibitors also enhance an electron paramagnetic resonance signal near g = 2 in anaerobic, submitochondrial particles from skunk cabbage, which appears to be specific to the alternate oxidase and thus provides a means for its assay.

Cyanides↗
PubMed1971

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.

Journal Article↗
PubMed1971

Studies of electron transport in dry and imbibed peanut embryos.

The respiration of isolated peanut (Arachis hypogea) embryos has been studied with dry and wet embryos and mitochondria prepared after various times of imbibition. Dry seeds respire slowly, apparently via a respiratory chain which is deficient in cytochrome c. Cytochrome c-deficient mitochondria have been prepared from the embryos up to 16 hours following imbibition. These mitochondria can metabolize reduced nicotinamide adenine dinucleotide and succinate, without respiratory control by ADP, but they do phosphorylate. Added cytochrome c increases both respiration and phosphorylation of these embryonic mitochondria. When growth starts, mitochondria appear which are similar to those isolated from other mature plant tissues; they have respiratory control and can actively metabolize succinate, malate, and reduced nicotinamide adenine dinucleotide. These latter mitochondria contain a concentration of cytochrome c comparable to that found in mitochondria isolated from other mature plant tissues. It is suggested that the earliest type of mitochondria may be required to control respiration in the dry and the recently wetted embryo.

Journal Article↗
PubMed1970

Effects of guanidine inhibitors on mung bean mitochondria.

The effects of phenylethylbiguanidide, decamethylenediguanidide, and octylguanidine have been studied with mung bean hypocotyl mitochondria (Phaseolus aureus var. Jumbo) supplied with malate, reduced nicotinamide adenine dinucleotide, succinate, or ascorbate-tetramethyl-p-phenylenediamine as substrates. The guanidines act as energy transfer inhibitors, all three inhibiting all three phosphorylation sites. Phenylethylbiguanidide causes only partial inhibition even at relatively high concentrations. Decamethylenediguanidide inhibits about 70% of the malate respiration, 55% of the succinate respiration, and 35% of the ascorbate-tetramethyl-p-phenylenediamine respiration.Octylguanidine inhibits all three phosphorylation sites and the cyanide-insensitive respiration, but to differing extents and at different concentrations. Both states 3 and 4 are inhibited by octylguanidine. Inhibition of state 4 is preceded by an uncoupling action at lower concentrations of inhibitor, while inhibition of state 3 is influenced by the state of the mitochondria when the inhibitor is added. Application of the guanidine to state 4 mitochondria is more effective than application to mitochondria already in state 3.

Journal Article↗
PubMed1970

Preparation and some properties of submitochondrial particles from tightly coupled mung bean mitochondria.

Osmotic shock was found to be better than freezing and thawing, a French press, or sonic oscillation for the preparation of submitochondrial particles from mung bean (Phaseolus aureus) hypocotyl mitochondria. Particles prepared by osmotic shock rapidly oxidize reduced nicotinamide adenine dinucleotide and succinate, but they oxidize malate slowly. NADH oxidation was slightly stimulated by cytochrome c, ATP, and ADP; succinate oxidation was markedly increased by ATP, slightly by ADP and cytochrome c; and malate oxidation required the addition of NAD(+) NADH oxidation is inhibited weakly by amytal, completely by antimycin A and KCN, but not by rotenone. Chlorsuccinate, malonate, antimycin A, and KCN inhibit succinate oxidation. The action of antimycin A and KCN is incomplete, while chlorsuccinate and malonate were competitive inhibitors. Antimycin A combined stoichiometrically with particle protein in the ratio of 0.23 millimicromole per milligram of protein.Oligomycin and bis(hexafluoroacetonitryl) acetone, a potent uncoupler of oxidative phosphorylation, were without effect on oxygen uptake but did influence the ATP-stimulated onset of respiration when succinate was substrate. Fresh particles were markedly inhibited by oxtylguanidine, indicating energy conservation, but this inhibition decreased on storage of the particles.Spectra show the presence of cytochrome components the same as those of the intact mung bean mitochondrion, but present at higher concentrations. The molar concentrations of the particle cytochromes were two to three times those of the intact mitochondrion and the molar ratios were calculated as 0.9:1.0:1.0:2.8 for cytochromes a:b:c:flavoprotein, respectively.

Journal Article↗
PubMed1970

Energy-linked Functions of Submitochondrial Particles Prepared from Mung Bean Mitochondria.

Submitochondrial particles from mung bean mitochondria (Phaseolus aureus) are able to catalyze an energy-linked reduced nicotinamide adenine dinucleotide-nicotinamide adenine dinucleotide phosphate transhydrogenase reaction supported by ATP or by aerobically generated high energy intermediates. The energy transfer pathway appears to differ from that utilized for oxidative phosphorylation.Mung bean submitochondrial particles will also reduce nicotinamide adenine dinucleotide by reversed electron transport from succinate or ascorbate tetramethyl-p-phenylenediamine. The energy requirement can be met by ATP or by aerobically generated high energy intermediates.A scheme for the energy transduction pathway in mung beans is postulated from the effects of inhibitors and uncouplers of energy transfer on transhydrogenase and reversed electron transfer reactions.

Journal Article↗
PubMed1968

The respiratory chain components of higher plant mitochondria.

TIGHTLY COUPLED MITOCHONDRIA HAVE BEEN PREPARED FROM A VARIETY OF PLANT SOURCES: white potato (Solanum tuberosum), Jerusalem artichoke (Heliantus tuberosus), cauliflower buds (Brassica oleracea), and mung bean hypocotyls (Phaseolus aureus). Mitochondria with no appreciable coupling were also prepared from skunk cabbage spadices (Symplocarpus foetidus).Room temperature difference spectra show that these mitochondria are very similar in the qualitative and quantitative composition of their electron carriers. The different cytochromes are present in the amounts of 0.1 to 0.3 mmumole per mg of mitochondrial protein. The molar ratios of the different electron carriers are, on the average: 0.7:0.7:1.0:3 to 4:10 to 15 respectively for cytochrome aa(3), cytochromes b, cytochromes c, flavoproteins, and pyridine nucleotides.From low temperature difference spectra carried out under particular experimental conditions, it can be deduced that these mitochondria contain 3 b cytochromes whose alpha bands are located at 552, 557, and 561 mmu, and 2 c cytochromes, one of which, a c(1)-like cytochrome, is firmly bound to the mitochondrial membrane. Cytochrome oxidase can be optically resolved into its 2 components a and a(3).For all kinds of mitochondria, the rates of oxidation of succinate are similar as well as the turnover of cytochrome oxidase (50-70 sec(-1)), regardless of the metabolic activities of the tissues. The number of mitochondria per cell appears to be the controlling factor of the intensity of tissue respiration.

Journal Article↗