Biomedical subjects
Publications and source records attributed to S B Wilson.
Mitochondrial respiration and oxidative phosphorylation were inhibited by the membrane potential probe 3,3'-dipropylthiocarbocyanine [diS-C3-(5)]. Evidence is presented that suggests that the dye acts as both an inhibitor of electron transport and an uncoupler of oxidative phosphorylation.
Freshly prepared washed or purified mung-bean (Phaseolus aureus) mitochondria utilize oxygen with ascorbate/tetramethyl-p-phenylenediamine mixture as electron donor in the presence of KCN. ATP control of the oxygen uptake can be observed with very fresh mitochondria. The electron flow, which is inhibited by antimycin A, salicylhydroxamic acid or octylguanidine, takes place by reversed electron transport through phosphorylation site II and thence to oxygen through the cyanide-insensitive pathway. Oligomycin and low concentrations of uncoupler partially inhibit the oxygen uptake in a manner similar to that observed for other energy-linked functions of plant mitochondria. An antimycin A-insensitive oxygen uptake occurs if high concentrations of uncoupler are used, indicating that the pathway of electron flow has been altered. The process of cyanide-insensitive ascorbate oxidation is self-starting, and, since it occurs in the presence of oligomycin, it is concluded that the reaction can be energized by a single energy-conservation site associated with the cyanide-insensitive oxidase pathway.
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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.
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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.
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.
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.
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The potential risk of surface and ground water contamination by phosphorus (P) and heavy metals leached from compost-based containerized media has become an environmental concern. Solubility and fractionation of P and heavy metals were evaluated in media containing 0, 25, 50, 75, or 100% compost derived from biosolids and yard trimmings for potential impacts on the environment. As compost proportion in peat-based media increased from 0 to 100%, concentrations of total P, Cd, Cu, Ni, Pb, Zn, and Mn in the media increased whereas concentrations of total Co and Cr decreased. Except for Cu, all heavy metals in the water-soluble fraction decreased with increasing compost proportion in the media, because of higher Fe, Al, and Ca concentrations and pH values of the composts than the peat. When the media pH is controlled and maintained at normal range of plant growth (5.5-6.5), leaching of the heavy metals is minimal. Incorporation of compost to the peat-based media also decreased the proportion of total P that was water-soluble. However, concentrations of bioavailable inorganic phosphorus (NaHCO3-IP), readily mineralizable organic phosphorus (NaHCO3-OP), potentially bioavailable inorganic phosphorus (NaOH-IP), and potentially bioavailable organic phosphorus (NaOH-OP) were still higher in the media amended with compost because of higher total P concentration in the compost. Further study is needed to verify if less or no topdressing of chemical P fertilizer should be applied to the compost-amended media to minimize P effect on the environment when compost-amended potting media are used for nursery or greenhouse crop production systems.