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Biomedical subjects

W D Bonner

Publications and source records attributed to W D Bonner.

At least 37 records · Page 2Linked to original sources
PubMed1977

EPR studies of higher plant mitochondria. I Ubisemiquinone and its relation to alternative respiratory oxidations.

An EPR investigation of the region of the higher plant respiratory chain involving ubiquinone and Center S-3 of succinate dehydrogenase is reported. At temperatures close to those of liquid helium, first derivative spectra corresponding to Center S-3 (gmax = 2.017) and a signal split around g = 2.00 (major features of peaks and troughs at g values of 2.045, 2.03, 1.985, 1.97 and 1.96) were observed in mung bean (Phaseolus aureus), Arum maculatum spadix, Sauromatum guttatum spadix and tulip bulb (Tulipa gesnerana) mitochondria. The split signal was small or absent in potato tuber and Symplocarpus foetidus spadix mitochondria. The redox behavior of these signals in mung bean mitochondria in a variety of respiratory steady-state conditions suggested that the components giving rise to them were an integral part of the respiratory chain and were located on the substrate side of coupling Site II. The split signal could be removed by addition of hydroxamic acids in all tissues tested, although the Ks of this effect was an order of magnitude higher than the Ki of inhibition of the alternative respiratory pathway in mung bean and Sauromatum guttatum spadix mitochondria. The results are discussed in relation to the current ideas on the ordering of components in the region around the classical Site II of the respiratory chain and in relation to the location of the alternative respiratory oxidase pathway of higher plants.

Cyanides↗
PubMed1977

The effect of calcium on the respiratory responses of mung bean mitochondria.

Purified mung bean hypocotyl mitochondria were examined for their capacity to carry out respiration-dependent accumulation of calcium. The addition of 0.1-1.0 mM calcium to mung bean mitochondria supplemented with succinate gave no stimulation of state 4 respiration even in the presence of inorganic phosphate and the ionophoretic antibiotic A-23187. Even at high calcium concentrations, no transient changes in the respiratory activity occurred and subsequent addition of ADP initiated a further state 3 response. Although the additions of calcium resulted in a rapid H+ ejection, it was insensitive to lanthanum and uncoupling agents. Similarly, additions of calcium failed to initiate any transient changes in the oxidation-reduction states of either pyridine nucleotides or cytochrome b. Direct spectrophotometric recordings of absorbance changes of murexide revealed no respiration-linked calcium transport. It is proposed that although mung bean mitochondria possess a respiration-linked electrochemical potential gradient it would appear that this potential cannot be expressed as calcium transport even at high ion concentrations, probably due to a low calcium membrane permeability.

Anaerobiosis↗
PubMed1977

Involvement of iron in the biogenesis of the cyanide-insensitive respiration in the yeast Saccharomycopsis lipolytica.

The involvement of iron in the biogenesis of the cyanide-insensitive respiration in the yeast Saccharomycopsis lipolytica has been established on the following basis: (1) endogenous metal chelation by either benzyl- or salicylhydroxamic acid, EDTA or nitrilotriacetate prevented the biogenesis of the cyanide-insensitive respiratory pathway in S. lipolytica. (2) Addition of Fe(III) during the biogenesis increased both the rate of the appearance of the alternative respiratory pathway and its extent. Neither Fe(II), nor Co(II), Cu(II), Al(III), La(III), Mn(II) or Mg(II) could substitute for Fe(III). (3) The biogenesis of the alternative respiratory pathway could be dissociated into two steps: (a) a first one, slow, cycloheximide-sensitive, temperature-dependent, iron-independent, leading to cells still fully cyanide-sensitive, presumably involving the de novo biosynthesis of an inactive protein moiety and (b) a second step, fast, iron-dependent, temperature-independent, cycloheximide-insensitive, leading to cells with a cyanide-insensitive respiration, presumably the activation by iron of the inactive precursor.

Chelating Agents↗
PubMed1977

The effects of bathophenanthroline, bathophenanthrolinesulphonate and 2-thenoyltrifluoroacetone on mung-bean mitochondria and submitochondrial particles.

The effects of bathophenanthroline, bathophenanthrolinesulphonate and 2-thenoyltrifluoroacetone on mung-bean mitochondria and submitochondrial particles were investigated. A variety of inhibitory effects on the oxidations of NADH, succinate and malate were observed. The results are discussed in relation to sites of inhibition and their relation to the effects on mammalian mitochondria.

Malates↗
PubMed1975

Biochemical characteristics of the outer membranes of plant mitochondria.

Like the outer membranes of liver mitochondria, those of plant mitochondria are impermeable to cytochrome c when intact and can be ruptured by osmotic shock. Isolated plant outer mitochondrial membranes are also similar to the corresponding liver membranes in terms of phospholipid and sterol content. Sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis experiments indicate that a single class of proteins (apparent molecular weight 30 000) comprises the bulk of the plant outer membrane protein. There are also considerable amounts of polysaccharide associated with these membranes, which may contribute to their osmotic stability.

Calcium↗
PubMed1974

On the lack of ATP-induced midpoint potential shift for cytochrome b-566 in plant mitochondria.

Recently proposed mechanisms of site II energy transduction that assign a key role to cytochrome b-566 are based on the finding that the apparent midpoint potential of b-566 in animal mitochondria increases by more than 250 mV upon addition of ATP [Chance et al. (1970) Proc. Nat. Acad. Sci. USA 66, 1175-1182]. However, since it has never been shown that the redox mediators used in the midpoint potential measurements equilibrate directly with b-566, the observed midpoint potential shift could merely reflect reversed electron transport. In mung bean mitochondria, the apparent midpoint potential of b-566 is known to be unaffected by addition of ATP [Dutton and Storey (1971) Plant Physiol. 47, 282-288]. In the present work, mung bean b-566 is shown to undergo an ATP-induced reduction similar to that observed for b-566 in animal mitochondria. However, in mung bean mitochondria the reduction is found to be rapidly relaxed by addition of redox mediator (phenazine methosulfate, PMS) and concomitantly PMS causes a marked, antimycinsensitive stimulation of ATPase activity. These results suggest that the ATP-induced reduction in mung bean mitochondria is due to reversed electron transport and that PMS can effectively short-circuit reversed electron transport in this system, bringing it close to equilibrium. Moreover, since mung bean and animal b-566 are identical in all other respects tested, the results support the idea that the apparent midpoint potential shift in animal mitochondria is also merely due to reversed electron transport, and that the mediators are now not effective enough to bring the system to equilibrium.

Adenosine Triphosphatases↗