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J M Gould

Publications and source records attributed to J M Gould.

At least 37 records · Page 2Linked to original sources
PubMed1983

Substrate-induced H2O2 production in mycelia from the lignin-degrading fungus Phanerochaete chrysosporium.

Broken and subsequently washed mycelia from the lignin-degrading fungus Phanerochaete chrysosporium generated increased levels of H2O2 when exposed to a lignocellulosic substrate (ground wheat straw) or substrate analogue (Poly B-411). H2O2 production was observed only in cultures grown on limiting nitrogen, a condition known to induce the lignin-degrading activity of this organism. H2O2 production was observed in the pH range of 4.5 to 8.4, but the highest levels of H2O2 were generated around pH 6. The mycelia also exhibited catalase activity, which was 5- to 10-fold higher in nitrogen-limited cultures.

Agaricales↗
PubMed1982

Characterization of lignin in situ by photoacoustic spectroscopy.

Photoacoustic spectroscopy is a recently developed nondestructive analytical technique that provides ultraviolet, visible, and infrared absorption spectra from intensely light scattering, solid, and/or optically opaque materials not suitable for conventional spectrophotometric analysis. In wood and other lignocellulosics, the principal ultraviolet absorption bands, in the absence of photosynthetic pigments, arise from the aromatic lignin component of the cell walls. Photoacoustic spectra of extracted lignin fragments (milled wood lignin) and synthetic lignin-like polymers contain a single major absorption band at 280 nanometers with an absorption tail extending beyond 400 nanometers. Photoacoustic spectra of pine, maple, and oak lignin in situ contain a broad primary absorption band at 300 nanometers and a longer wavelength shoulder around 370 nanometers. Wheat lignin in situ, on the other hand, exhibits two principle absorption peaks, at 280 nanometers and 320 nanometers. The presence of absorption bands at wavelengths greater than 300 nanometers in intact lignin could result from (a) interacting, nonconjugated chromophores, or (b) the presence of more highly conjugated structural components formed as the result of oxidation of the polymer. Evidence for the latter comes from the observation that, on the outer surface of senescent, field-dried wheat culms (stems), new absorption bands in the 350 to 400 nanometer region predominate. These new bands are less apparent on the outer surface of presenescent wheat culms and are virtually absent on the inner surface of either senescent or presenescent culms, suggesting that the appearance of longer wavelength absorption bands in senescent wheat is the result of accumulated photochemical modifications of the ligin polymer. These studies also demonstrate photoacoustic spectroscopy to be an important new tool for the investigation of insoluble plant components.

Journal Article↗
PubMed1981

Kinetics of hydrogen ion diffusion across phospholipid vesicle membranes.

The membrane-impermeant, pH-sensitive fluorescence probe 8-hydroxy-1,3,6-pyrenetrisulfonate can be entrapped within the internal aqueous compartment of unilamellar phospholipid vesicles, where it serves as a reliable indicator of internal aqueous hydrogen ion concentration [Clement, N. R., & Gould, J. M. (1981) Biochemistry 20, 1534-1539]. When the external (medium) pH of a suspension of soybean phospholipid vesicles was rapidly changed from 8.2 to 6.65, the rate of subsequent H+ influx into the vesicles, measured as the change in pyranine fluorescence, was limited (in KCl media) by the rate of charge-compensating counterion redistributions. The half-time for the pyranine fluorescence change (corresponding to an internal pH change from 8.2 to 7.43), which was several minutes in the absence of valinomycin, could be decreased to approximately 300 ms, but not further, by the K+ ionophore valinomycin. Proton ionophores such as gramicidin or bis(hexafluoroacetonyl)acetone (1799), on the other hand, decreased the time required for transmembrane H+ equilibration to less than 1 ms. These findings indicate that the intrinsic permeability of unilamellar vesicle membranes to hydrogen ions is surprisingly high and much greater than the observed permeabilities of other small ions.

Arylsulfonates↗
PubMed1981

Pyranine (8-hydroxy-1,3,6-pyrenetrisulfonate) as a probe of internal aqueous hydrogen ion concentration in phospholipid vesicles.

The fluorescence intensity (at 510 nm) of the hydrophilic pyrene analogue 8-hydroxy-1,3,6-pyrenetrisulfonate (pyranine) is strongly dependent upon the degree of ionization of the 8-hydroxyl group (pKa = 7.2) and hence upon the medium pH, over the range pH 6--10. Because of its polyanionic character, pyranine does not bind significantly to phospholipid vesicles having a net anionic surface charge. As a result, it is possible to form vesicles in the presence of pyranine which, after removal of external probe by gel filtration, contain pyranine entrapped within the internal aqueous compartment. Once entrapped, pyranine does not readily leak out of the vesicles. Because the fluorescence properties of entrapped pyranine resemble closely the properties of bulk pyranine solution with respect to pH sensitivity, pyranine can be used as a reliable reporter of aqueous pH changes within anionic vesicles. When HCl is rapidly added to a suspension of unilamellar soybean phospholipid (asolectin) vesicles preincubated at alkaline pH, a biphasic decrease in the pH of the vesicle inner aqueous compartment is observed. An initial, very rapid and electrically uncompensated H+ influx (t 1/2 less than 1 s) results in the generation of a transmembrane electric potential opposing further H+ influx. This leads to the development of a much slower (t 1/2 approximately equal to 5 min), valinomycin-sensitive, proton--counterion exchange which continues until the proton concentration gradient is eliminated. Similar results were obtained in asolectin vesicles prepared by detergent dilution, in sonicated egg phosphatidylcholine vesicles, and in multilamellar asolectin liposomes. The rather high permeability of soybean lipid membranes to H+ is surprising in view of the widespread use of these lipids for the reconstitution of membrane proteins which are thought to generate or utilize H+ ion gradients in energy transduction reactions.

Arylsulfonates↗
PubMed1981

Kinetics for development of gramicidin-induced ion permeability in unilamellar phospholipid vesicles.

Two kinetics for the development of gramicidin-dependent cation permeability in small unilamellar vesicles have been studied by using a vesicle-entrapped, pH-sensitive fluorescence probe to continuously report changes in intravesicular pH. The incorporation of 4-5 gramicidin dimers/vesicle was sufficient to increase the proton and counterion permeability of that vesicle by several orders of magnitude, so that ionic equilibration following a perturbation of the external medium pH occurred in less than 1 s. Once a functional gramicidin dimer has become incorporated into one vesicle, it does not readily exchange into another, so that the effects of gramicidin with regard to an individual vesicle can be considered to be essentially "all or none." The rate at which transmembrane ion permeability develops in a vesicle suspension was found to depend upon the degree of fluidity of the membrane hydrocarbon interior, being much lower at low temperatures or when cholesterol was present in the bilayer. Low temperatures and increasing bilayer cholesterol content also decreased the number of vesicles affected by a given gramicidin concentration, indicating a decreased membrane solubility for the ionophore at low bilayer fluidities.

Arylsulfonates↗
PubMed1980

Proton efflux through the chloroplast ATP synthase (CF0 . CF1) in the presence of sulfhydryl-modifying agents.

The rate of photosynthetic electron transport measured in the absence of ADP and Pi is stimulated by low levels of Hg2+ or Ag+ (50% stimulation approximately or equal to 3 Hg2+ or 6 Ag+/100 chlorophyll) to a plateau equal to the transport rate under normal phosphorylating conditions (i.e. +ADP, +Pi). Chloroplasts pretreated in the light under energizing conditions with N-ethylmaleimide show a similar stimulation of non-phosphorylating electron transport. The stimulations of non-phosphorylating electron transport by Hg2+, Ag+ and N-ethylmaleimide are reversed by the CF1 inhibitor phlorizin, the CF0 inhibitor triphenyltin chloride, and can be further stimulated by uncouplers such as methylamine. The Hg2+ and N-ethylmalemide stimulations, but not the Ag+ stimulation, are completely reversed by low levels of ADP (2 microM), ATP (2 microM), AND Pi (400 microM). Ag+, which is a potent inhibitor of ATP synthesis, has little or no effect upon phosphorylating electron transport (+ADP, +Pi). Concomitant with the stimulations of non-phosphorylating electron transport by Hg2+, Ag+ and ADP + Pi, there is a decrease in the level of membrane energization (as measured by atebrin fluorescence quenching) which is reversed when the CF0 channel is blocked by triphenyltin. These results suggest that modification of critical CF1 sulfhydryl residues by Hg2+, Ag+ or N-ethylmalemide leads to the loss of intra-enzyme coupling between the transmembrane proton-transferring and the ATP synthesis activities of the CF0-CF1 ATP synthase complex.

ATP Synthetase Complexes↗
PubMed1979

Respiration-linked proton transport, changes in external pH, and membrane energization in cells of Escherichia coli.

The kinetics of respiration-dependent proton efflux and membrane energization have been studied in intact cells of logarithmic-phase Escherichia coli. Parallel measurements of the rate and extent of proton efflux into the external medium (half-time, about 10 s; ratio of H(+) to O, about 0.5) and the oxidation of E. coli cytochrome b (half-time, </=1 s; about 6% oxidized) after a pulse of 5.5 ng-atoms of O indicate that the rate of proton efflux is at least 10 times slower than expected from the time required for the cells to reduce the oxygen added in the pulse. The kinetics of formation and dissipation of the transmembrane electric potential (deltapsi) after an O(2) pulse were estimated from changes in the fluorescence properties of the cell envelope-bound probe N-phenyl-1-naphthylamine. Under anaerobic conditions, a small pulse of oxygen induced a rapid (half-time, </=1 s) partial decrease in the fluorescence intensity of the probe, followed by a slower relaxation of the fluorescence change to the original intensity. The extent of the initial rapid decrease was linearly dependent upon the amount of oxygen added in the pulse (0 to 11 ng-atoms of O per pulse), whereas the rate of the subsequent relaxation was accelerated by the uncoupler p-trifluoromethoxycarbonylcyanidephenylhydrazone and the K(+) ionophore colicin E1. This suggests that the initial fluorescence decrease after an O(2) pulse reflects the energization of the membrane, whereas the relaxation of the fluorescence decrease reflects the subsequent deenergization of the membrane arising from counterion redistributions. The fact that the efflux of H(+) into the external medium after an O(2) pulse was inefficient and much slower (half-time, about 10 s) than the reduction of the added O(2) (half-time, </=1 s) and the energization of the membrane (half-time </=1 s) suggests that some of the protons translocated across the cytoplasmic membrane during a brief pulse of respiratory activity are accumulated in a region of the cell which is not in rapid equilibrium with the external medium.

Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone↗
PubMed1978

The kinetics of oxygen-induced proton efflux and membrane energization in Escherichia coli.

The kinetics of respiration-dependent proton efflux and membrane energization have been studied in intact cells of logarithmic phase Escherichia coli. Proton efflux following a small O2 pulse is slow (t1/2 approximately equal to 10 sec) and inefficient (H+/O approximately equal to 0.5), taking 5-10 times longer than expected from the time required for the cells to reduce the O2 added in the pulse. A much closer agreement is found in cells treated to enhance counter ion fluxes and eliminate the transmembrane electric potential (deltapsi). In cells treated with SCN-, or with colicin E1 (which enhances K+ permeability), the rates of proton efflux are much faster (t1/2 less than or equal to 1 sec) than in untreated cells. The kinetics of formation and dissipation of deltapsi were estimated from changes in the fluorescence properties of the cell envelope bound probe N-phenyl-l-naphthylamine. In untreated cells, a small O2 pulse induces a rapid (t1/2 less than or equal to 0.5 sec) decrease in fluorescence intensity followed by a slower (t1/2 approximately equal to 40 sec) return of the fluorescence to the original level. The extent of the initial fluorescence decrease is proportional to the amount of O2 added, although the half-time for the relaxation is independent of the amount of O2 added. Colicin E1 (plus K+) and the uncoupler FCCP greatly decrease the half-time of the relaxation, while only slightly affecting the extent of the initial decrease, indicating that the initial fluorescence decrease is reporting the energization of the membrane while its relaxation is reporting the subsequent deenergization of the membrane resulting from counterion redistributions. The fact that the efflux of H+ into the medium after an O2 pulse is small and much slower (t1/2 approximately equal to 10 sec) than the actual energization of the membrane (t1/2 less than or equal to 0.5 sec) suggests that the current of respiratory H+ involved in membrane energization is confined within the bacterial cell envelope.

1-Naphthylamine↗
PubMed1976

Inhibition by triphenyltin chloride of a tightly-bound membrane component involved in photophosphorylation.

At very low concentrations (less than 1 muM) triphenyltin chloride inhibits ATP formation and coupled electron transport in isolated spinach chloroplasts. Basal (-Pi) and uncoupled electron transport are not affected by triphenyltin. The membrane-bount ATP in equilibrium Pi exchange and Mg2+-dependent ATPase activities of chloroplasts are also completely sensitive to triphenyltin, although the Ca2+-dependent and Mg2+-dependent ATPase activities of the isolated coupling factor protein are insensitive to triphenyltin. The light-driven proton pump in chloroplasts is stimulated (up to 60%) by low levels of triphenyltin. Indeed, the amount of triphenyltin necessary to inhibit ATP formation or stimulate proton uptake is dependent upon the amount of chloroplasts present in the reaction mixture, with an apparent stoichiometry of 2-2.5 triphenyltin molecules/100 chlorophyll molecules at 50% inhibition of ATP formation and half-maximal stimulation of proton uptake. Chloroplasts partially stripped of coupling factor by an EDTA was are no longer able to accumulate protons in the light. However, low levels of triphenyltin can effectively restore this ability. The amount of triphenyltin required for the restoration of net proton uptake is also dependent upon the amount of chloroplasts, with a stoichiometry of 4-5 triphenyltin molecules/100 chlorophyll molecules at 50% reconstitution. On the basis of this and other evidence it is concluded that triphenyltin chloride inhibits phosphorylation, ATP + Pi exchange and membrane-bound ATPase activities in chloroplasts by specifically blocking the transport of protons through a membrane-bound carrier or channel located in a hydrophobic region of the membrane at or near the functional binding site for the coupling factor.

Adenosine Triphosphatases↗