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W D Bonner

Publications and source records attributed to W D Bonner.

65 records · Page 4Linked to original sources
PubMed1967

Properties of Higher Plant Mitochondria. I. Isolation and Some Characteristics of Tightly-coupled Mitochondria from Dark-grown Mung Bean Hypocotyls.

The mitochondria isolated from dark-grown mung bean hypocotyls oxidize succinate, l-malate, and externally added reduced nicotine adenine dinucleotide (NADH) with good respiratory control. While the pattern of respiration resembles that of animal mitochondria, there are 4 basic differences between the respiratory properties of mung bean and animal mitochondria: A) the ability to oxidize NADH, B) the pattern of succinate and malate oxidation, C) the rate of oxygen uptake, and D) the adenosine-5'-diphosphate to oxygen ratios.The apparent ;Km' for malate of mung bean mitochondria is about one order higher than that expected from malic dehydrogenase in animal mitochondria, whereas the affinity for phosphate is about 5 times higher with plant mitochondria than rat-liver mitochondria. While the half-maximal stimulation of respiration by adenosine-5'-diphosphate is practically identical to that of animal mitochondria, higher concentrations of adenosine-5'-diphosphate cause some decrease in its stimulating action.

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PubMed1967

Properties of Higher Plant Mitochondria. II. Effects of DNP, m-Cl-CCP, and Oligomycin on Respiration of Mung Bean Mitochondria.

Effects of inhibitors of phosphorylation on the oxidation of succinate and of l-malate were investigated with tightly coupled mitochondria isolated from mung bean hypocotyls. When mitochondria were incubated with 2,4-dinitrophenol, or carbonyl cyanide m-chlorophenylhydrazone prior to the addition of substrate, the uncoupling effects of these chemicals were relatively small. This is probably caused by relative lack in these mitochondria of endogenous substrates, ATP, and/or "high-energy intermediates". The action of uncoupling agents is, therefore, revealed in a more striking manner when they are introduced during the second state 4. Of the 2 uncoupling agents tested, malate oxidation consistently required 1.5 to 2 times higher concentration of the agents for the half-maximal effects than succinate oxidation. From the comparison of the degree of uncoupling it is concluded that 2,4-dinitrophenol is a better uncoupler of succinate oxidation, whereas carbonyl cyanide m-chlorophenylhydrazone functions as a more complete uncoupler of malate oxidation.Oligomycin does not inhibit state 4 rates, while the increment of respiration due to added ADP is completely inhibited by this antibiotic. Identical half-maximal effects are observed with the same concentration of oligomycin in both succinate and l-malate oxidation. The oligomycin effect depends on the mitochondrial concentration employed. The concentration of this chemical required for the half-maximal effect is 55 to 80 mmumoles per mg mitochondrial protein. It is suggested that this inhibitor of phosphorylation binds all of the phosphorylation sites regardless of whether the sites are functional or not.

Journal Article↗
PubMed1967

Properties of Higher Plant Mitochondria. III. Effects of Respiratory Inhibitors.

The effects of representative respiratory inhibitors were investigated on the coupled respiration of mung bean mitochondria using succinate and l-malate as substrates. The inhibitors studied were: (I) malonate, (II) amytal and rotenone, (III) antimycin A and 2-n-nonyl-4-hydroxyquinoline N-oxide (NOQNO), and (IV) cyanide and azide.Malonate inhibition of succinate oxidation follows a classical type of competitive inhibition with an inhibitor dissociation constant of 0.13 mm. There is no inhibition detectable when malate is used as substrate. In contrast to animal mitochondria, amytal is capable of inhibiting 20 to 40% of succinate oxidation and 90 to 100% of malate oxidation, but inhibition due to rotenone amounts to only 0 to 20% of succinate oxidation and 40 to 50% of malate oxidation. The half-maximal inhibition caused by amytal occurs at 2 to 2.5 mm and that by rotenone at 3 mmumoles/mg protein.The maximal inhibition caused by either antimycin A or NOQNO is 70 to 80% of the state 3 respiration. Very little inhibition was observed on the state 4 respiration, and both inhibitors were capable of titrating stoichiometrically with mitochondrial protein with identical titers, 0.22 mmumoles/mg protein for half-maximal inhibition. They differ, however, in that NOQNO does uncouple oxidative phosphorylation in mung bean mitochondria, but antimycin A does not do so. Both cyanide and azide inhibit the state 3 rate 65 to 80%. Inhibition of state 4 respiration can be up to 50% by cyanide, while almost none by azide. Uncoupling action was noted with cyanide, but very little with azide.It is concluded that the second state 3 rate of succinate oxidation includes 80% succinoxidase, the remaining 20% being contributed by the NADH pathway. Malate oxidation apparently does not involve succinoxidase. Malate oxidation is completely sensitive to amytal, but only 50% inhibited by rotenone. A difference between animal and plant mitochondria appears to be in the flavoproteins associated with NADH oxidation.From the observations that antimycin A, NOQNO, cyanide, and azide do not cause complete inhibition, it is suggested that a leakage of electrons to oxygen exists before the site of inhibition of antimycin A or NOQNO.

Journal Article↗
PubMed1967

Peroxidase associated with higher plant mitochondria.

The presence of peroxidase in mitochondria from etiolated mung bean hypocotyls and skunk cabbage spadices, suggested by carbon monoxide difference spectra and the spectral response to methyl hydroperoxide, was shown to result from contamination of the isolated mitochondria by a denser particle fraction with high peroxidase activity. The mitochondria themselves have no peroxidatic activity. Analysis of the homogenate of mung bean hypocotyls revealed that over 90% of the peroxidase was soluble, as expected. Sonication of the isolated mitochondria, however, did not remove all the peroxidase from the particulate fraction, indicating that some of this enzyme is tightly bound to a membrane. These results suggest that the peroxidase in plant cells is localized in lysosomes or microbodies, most of which are ruptured on tissue homogenization to give soluble peroxidase, but some of which survive and appear as membrane bound peroxidase.

Lysosomes↗
PubMed1966

DNA from plant mitochondria.

DNA WAS ISOLATED FROM A MITOCHONDRIAL FRACTION OF EACH OF THE FOLLOWING PLANT MATERIALS: Mung bean (Phaseolus aureus) etiolated hypocotyl; turnip (Brassica rapa) root; sweet potato (Ipomoea batatas) root; and onion (Allium cepa) bulb. It was found that all of these mitochondrial fractions contained DNA, the densities of which were identical (rho=1.706 g.cm(-3)). An additional DNA (rho=1.695) band found in the mitochondrial fraction of Brassica rapa, was identical to DNA separately isolated from the chloroplast-rich fraction. The origin of the second DNA from Allium mitochondrial fraction was not identified.Contrary to the identity of the mitochondrial DNA, DNA from nuclear fractions differed not only with each other but from the corresponding mitochondrial DNA.DNA from Phaseolus and Brassica mitochondria showed the hyperchromicity characteristic of double stranded, native DNA upon heating; Tm's in 0.0195 Na(+) were the same; 72.0 degrees . The amount of DNA within the mitochondrion of Phaseolus was estimated to be 5.0 x 10(-10) mug; this estimate was made by isolating the mitochondrial DNA concomitantly with the known amount of added (15)N(2)H B. subtilis DNA (rho=1.740). Approximately the same amount of DNA was present in the mitochondrion of Brassica or Ipomoea.

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