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At least 829 records · Page 46Linked to original sources
PubMed1990

Competitive interaction of three peroxidizing herbicides with the binding of [3H]acifluorfen to corn etioplast membranes.

The specific binding of the herbicide acifluorfen 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid to corn etioplast membranes is competitively inhibited by protoporphyrinogen IX, the substrate of protoporphyrinogen oxidase. Three other peroxidizing molecules, oxadiazon [5-terbutyl-3-(2,4-dichloro-5-isopropoxyphenyl)-1,3,4-oxadiazol -2-one], LS 82556 [(S)3-N-(methylbenzyl)carbamoyl-5-propionyl-2,6-lutidine], and M&B 39279 [5-amino-4-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)pyrazol], also compete with acifluorfen for its binding site. The four herbicides thus bind to the same site, or to closely located sites, on the enzyme protoporphyrinogen oxidase.

Binding Sites↗
PubMed1990

AS-1 cyanophage infection inhibits the photosynthetic electron flow of photosystem II in Synechococcus sp. PCC 6301, a cyanobacterium.

In Synechococcus sp. cells AS-1 cyanophage infection gradually inhibits the photosystem II mediated photosynthetic electron flow whereas the activity of photosystem I is apparently unaffected by the cyanophage infection. Transient fluorescence induction and flash-induced delayed luminescence decay studies revealed that the inhibition may occur at the level of the secondary acceptor, QB of photosystem II. In addition, the breakdown of D1-protein is inhibited, comparable to DCMU-induced protection of D1-protein turnover, in AS-1-infected cells.

Chlorophyll↗
PubMed1993

Interaction of carbonyl cyanide m-chlorophenylhydrazone with the photosystem II acceptor side.

We show that CCCP, known as an uncoupler of photophosphorylation and an ADRY agent, inhibits FeCy photoreduction and coupled O2 evolution by isolated chloroplasts equally (I50 approximately 2 microM), but is practically without effect on the O2 evolution coupled with SiMo reduction within the 0.2-10 microM concentration range. CCCP has no effect on the nanosecond chlorophyll fluorescence in chloroplasts incubated at low light intensity, but decreases it at high light intensity. The electron transfer from reduced TMPD or duroquinol to methylviologen is resistant to CCCP. The efficiency of the CCCP inhibitory action on the FeCy photoreduction depends on the rate of electron flow, which is controlled by the light intensity. The data obtained show that CCCP is oxidized by the photosystem II donor side and is reduced by QP, competing for electrons with FeCy and the cytochrome blf complex.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1993

Photosynthesis modulates the sign of phototaxis of wild-type Chlamydomonas reinhardtii. Effects of red background illumination and 3-(3',4'-dichlorophenyl)-1,1-dimethylurea.

We have found that the sign of phototaxis, i.e. the direction of phototactic migration either towards or away from the light source, of wild-type Chlamydomonas reinhardtii depends on its photosynthetic activity. This accounts for the frequently reported transient positive phototaxis that precedes a negative phototaxis of wild-type cells, as well as the earlier observations that preillumination affects the sign of phototaxis. The bases for our conclusion are as follows. (1) The transient nature of phototaxis was preferentially observable with blue-green actinic light rather than with green actinic light. (2) Red background light induces negative phototaxis under the actinic-light conditions in which, without background light, Chlamydomonas cells show exclusively positive phototaxis. (3) Both the effect of red background light and the transient change in the sign of phototaxis were inhibited by 3-(3',4'-dichlorophenyl)-1,1-dimethylurea, a specific inhibitor of photosynthesis. The conclusion modifies the accepted view that photosynthesis does not link with the phototaxis of this microorganism, thus constituting a necessary part in elucidating mechanisms of algal phototaxis.

Animals↗
PubMed1990

Pyruvate-induced stimulation of nitrogenase activity in Aulosira fertilissima.

The effect of pyruvate on nitrogenase activity in the N2-fixing cyanobacterium Aulosira fertilissima has been studied. Addition of 0.01-1.0 mM concentrations of pyruvate to actively N2-fixing cultures stimulated the enzyme activity in light; the maximum stimulation was observed with 0.3 mM pyruvate. There was no detectable stimulation of nitrogenase activity in the dark. Addition of pyruvate had no effect on the growth rate. DCMU gradually inhibited nitrogenase activity, but supplementation of 0.3 mM pyruvate to such cultures restored normal activity. Furthermore, pyruvate-induced stimulation of nitrogenase activity was found to be stimulated by anaerobic conditions. The inactivation of nitrogenase activity by the addition of O2 was restored by pyruvate. From 14CO2 uptake studies it appears that the alga preferred to take up pyruvate even in the presence of 14CO2. Thus it appears that pyruvate is taken up and metabolized by the alga, which manifests the observed effects.

Carbon Dioxide↗
PubMed1987

Glucagon treatment of rats activates the respiratory chain of liver mitochondria at more than one site.

The rate of reduction of ferricyanide in the presence and absence of antimycin and ubiquinone-1 was measured using liver mitochondria from control and glucagon treated rats. Glucagon treatment was shown to increase electron flow from both NADH and succinate to ubiquinone, and from ubiquinone to cytochrome c. 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) was shown to inhibit the oxidation of glutamate + malate to a much greater extent than that of succinate or duroquinol. Spectral and kinetic studies confirmed that electron flow between NADH and ubiquinone was the primary site of action but that the interaction of the ubiquinone pool with complex 3 was also affected. The effects of various respiratory chain inhibitors on the rate of uncoupled oxidation of succinate and glutamate + malate by control and glucagon treated mitochondria were studied. The stimulation of respiration seen in the mitochondria from glucagon treated rats was maintained or increased as respiration was progressively inhibited with DCMU, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), 2-heptyl-4-hydroxyquinoline-n-oxide (HQNO) and colletotrichin, but greatly reduced when inhibition was produced with malonate or antimycin. These data were also shown to support the conclusion that glucagon treatment may cause some stimulation of electron flow through NADH dehydrogenase, succinate dehydrogenase and through the bc1 complex, probably at the point of interaction of the complexes with the ubiquinone pool. The effects of glucagon treatment on duroquinol oxidation and the inhibitor titrations could not be mimicked by increasing the matrix volume, nor totally reversed by aging of mitochondria. These are both processes that have been suggested as the means by which glucagon exerts its effects on the respiratory chain (Armston, A.E., Halestrap, A.P. and Scott, R.D., 1982, Biochim. Biophys. Acta 681, 429-439). It is concluded that an additional mechanism for regulating electron flow must exist and a change in lipid peroxidation of the inner mitochondrial membrane is suggested.

Animals↗