Biomedical subjects
J M Gould
Publications and source records attributed to J M Gould.
Congenital trypanosomiasis in a child born in London.
A female infant of 22 months was referred to the Hospital for Sick Children, London, because of delayed psychomotor development. Extensive investigations revealed no cause, but eventually trypanosomiasis was diagnosed. The infant had not been outside the UK, but her mother came from Zaire, where the disease is endemic, but had lived in Kinshasa, where there is no sleeping sickness. It is thought, that the mother may have been asymptomatically infected by a fresh-blood transfusion four years earlier, since no other source of infection was apparent.
Stimulation of respiration-linked proton efflux in Escherichia coli by carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP).
Explore the source record for details and available documents.
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.
Hg2+-induced turnover of the chloroplast ATP synthetase complex in the absence of ADP and phosphate.
Explore the source record for details and available documents.
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.
Relationship between oxygen-induced proton efflux and membrane energization in cells of Escherichia coli.
Explore the source record for details and available documents.
Studies on the depolarization of the Escherichia coli cell membrane by colicin E1.
Explore the source record for details and available documents.
The effect of colicin E1 on proton extrusion and the H+/0 ration in Escherichia coli.
Explore the source record for details and available documents.
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.
Inhbition of photosystem II-dependent phosphorylation in chloroplasts by mercurials.
Explore the source record for details and available documents.
The phosphorylation site associated with the oxidation of exogenous donors of electrons to photosystem I.
1. The Photosystem I-mediated transfer of electrons from diaminodurene, diaminotolune and reduced 2,6-dichlorophenolindophenol to methylviologen is optimal at pH 8-8.5, where phosphorylation is also maximal. In the presence of superoxide dismutase, the efficiency of phosphorylation rises from smaller than or equal to 0.1 at pH 6.5 to 0.6-0.7 at pH 8-8.5, regardless of the exogenous electron donor used. 2. The apparent Km (at pH 8.1) for diaminodurene is 6-10-minus 4 M and for diaminotoluene is 1.2- 10- minus 3 M. The concentrations of diaminodurene and diaminotoluene required to saturate the electron transport processes are greater than 2 mM and greater than 5 mM, respectively. At these higher electron donor concentrations the rates of electron transport are markedly increased by phosphorylation (1.5-fold) or by uncoupling conditions (2-fold). 3. Kinetic analysis of the transfer of electrons from reduced 2,6-dichlorophenolindophenol (DCIPH2) to methylviogen indicates that two reactions with very different apparent Km values for DCIPH2 are involved. The rates of electron flux through both pathways are increased by phosphorylation or uncoupling conditions although only one of the pathways is coupled to ATP formation. No similar complications are observed when diaminodurene or diaminotoluene serves as the electron donor. 4. In the diaminodurene yields methylviologen reaction, ATP formation and that part of the electron transport dependent upon ATP formation are partially inhibited by the energy transfer inhibitor HgC12. This partial inhibition of ATP formation rises to about 50 percent at less than 1 atom of mercury per 20 molecules of chlorophyll, then does not further increase until very much higher levels of mercury are added. 5. It is suggested that exogenous electron donors such as diaminodurene, diaminotoluene and DCIPH2 can substitute for an endogenous electron carrier in donating electrons to cytochrome f via the mercury-sensitive coupling site (Site I) located on the main electron-transporting chain. If this is so, there would seem to be no reason for postulating yet another coupling site on a side branch of the electron transport chain in order to account for cyclic photophosphorylation.