Transducing mechanisms between circadian clock and overt rhythms in Gonyaulax

1969 ◽  
Vol 47 (2) ◽  
pp. 299-308 ◽  
Author(s):  
Beatrice M. Sweeney
Keyword(s):  
Electron Flow ◽  
Calvin Cycle ◽  
Continuous Light ◽  
Adenosine Diphosphate ◽  
Inhibitory Effect ◽  
Hill Reaction ◽  
Enzyme Preparations ◽  
Dimethyl Urea ◽  
The Hill

In Gonyaulax polyedra it is possible to measure overt rhythms in luminescence, photosynthesis, and cell division. A common endogenous oscillator appears to control all three processes. The question of concern here is the manner in which the information regarding period and phase is transduced from oscillator to overt rhythm. In the rhythm of photosynthetic capacity, the path of electron flow through systems I and II appears not to be the site of transduction, since there is no rhythm in cells in flashing light, in the Hill reaction, or in sensitivity to such specific inhibitors as dichlorophenyl dimethyl urea (DCMU), and carbonyl cyanide m-chlorophenylhydrazone (CCmP). The probable site of control is in the Calvin cycle, since the activity of the first enzyme in this cycle, ribulose diphosphate dicarboxylase, varies with the phase of the cells from which the enzyme is derived. The low activity of this enzyme in crude extracts from cells in the night phase in continuous light can be overcome by increasing the concentration of bicarbonate in the reaction mixture. In vivo also, increasing the concentration of bicarbonate decreases the amplitude of the rhythm markedly. The activity of mixtures of extracts prepared during the day and the night phase is intermediate between that of either enzyme preparation alone, suggesting that the differences in activity are not caused by the presence of activators or inhibitors. The activity of ribulose diphosphate carboxylase is reduced by high temperature and by the presence of parachloromercuribenzonate (pCMB) and both adenosine triphosphate (ATP) and adenosine diphosphate (ADP), but differences in sensitivity to inhibitors between "day" and "night" enzyme preparations are not observed. The concentration of ATP extractable from cells does not vary with the phase of the rhythm.Transduction in the luminescent rhythm appears to be via changes in the mechanism by which luminescence is stimulated in vivo, since it is possible to obtain large and almost equal amounts of light from cells throughout the rhythmic cycle by the addition of acid. Eliciting luminescence in this way appears to bypass the normal mechanism of stimulation. This conclusion is strengthened by the observation that the inhibitory effect of light on cell luminescence is also eliminated when acid is used.

Light-induced inhibition of sporangial formation of Phytophthora infestans on potato leaves

1975 ◽  
Vol 53 (22) ◽  
pp. 2680-2686 ◽  
Author(s):  
Yigal Cohen ◽  
Helena Eyal ◽  
Tova Sadon
Keyword(s):  
Phytophthora Infestans ◽  
Blue Light ◽  
Red Light ◽  
Continuous Light ◽  
Inhibitory Effect ◽  
Hill Reaction ◽  
Light Conditions ◽  
Temperature Dependent ◽  
Dimethyl Urea ◽  
The Hill

Phytophthora infestans failed to produce sporangia on infected potato leaves under continuous light conditions. Blue light (λmax = 450 nm) was most inhibitory, while red light (λmax = 650 nm) was ineffective in inhibiting sporangial formation. Low intensity of blue light (3.7 μEinstein m−2 s−1) induced about 85% inhibition. The inhibitory effect of blue light upon sporulation was temperature dependent: it increased with rise in the temperature from 10 °C to 25 °C. 3,3,4-Dichlorophenyl-1,1-dimethyl urea (DCMU), which blocks the Hill reaction of photosynthesis, did not enable the fungus to sporulate on leaves under light conditions. Preceding dark treatments did not remove the inhibitory effect of blue light; this suggested that sporulation of the fungus is not a 'dark induction phenomenon.'

The Inhibition of Platelet Aggregation by an Aorta Intima Extract

1974 ◽  
Vol 32 (02/03) ◽  
pp. 417-431 ◽  
Author(s):  
A. du P Heyns ◽  
D. J van den Berg ◽  
G. M Potgieter ◽  
F. P Retief
Keyword(s):  
Platelet Aggregation ◽  
Degradation Products ◽  
Adenosine Diphosphate ◽  
Inhibitory Effect ◽  
Protective Role ◽  
Vascular Trauma ◽  
Wear And Tear ◽  
Sequential Addition ◽  
Aggregation Activity

SummaryThe platelet aggregating activity of extracts of different layers of the arterial wall was compared to that of Achilles tendon. Arterial media and tendon extracts, adjusted to equivalent protein content as an index of concentration, aggregated platelets to the same extent but an arterial intima extract did not aggregate platelets. Platelet aggregation induced by collagen could be inhibited by mixing with intima extract, but only to a maximum of about 80%. Pre-mixing adenosine diphosphate (ADP) with intima extracts diminished the platelet aggregation activity of the ADP. Depending on the relationship between ADP and intima extract concentrations aggregating activity could either be completely inhibited or inhibition abolished. Incubation of ADP with intima extract and subsequent separation of degradation products by paper chromatography, demonstrated a time-dependent breakdown of ADP with AMP, adenosine, inosine and hypoxanthine as metabolic products; ADP removal was complete. Collagen, thrombin and adrenaline aggregate platelets mainly by endogenous ADP of the release reaction. Results of experiments comparing inhibition of aggregation caused by premixing aggregating agent with intima extract, before exposure to platelets, and the sequential addition of first the intima extract and then aggregating agent to platelets, suggest that the inhibitory effect of intima extract results from ADP breakdown. It is suggested that this ADP degradation by intima extract may play a protective role in vivo by limiting the size of platelet aggregates forming at the site of minimal “wear and tear” vascular trauma.

Interaction of Photosystem II Herbicides with Bicarbonate and Formate in Their Effects on Photosynthetic Electron Flow

1984 ◽  
Vol 39 (5) ◽  
pp. 374-377 ◽  
Author(s):  
J. J. S. van Rensen
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Electron Flow ◽  
Photosynthetic Electron Transport ◽  
Hill Reaction ◽  
Amaranthus Hybridus ◽  
Apparent Affinity ◽  
Photosynthetic Electron Flow ◽  
Different Characteristics ◽  
The Hill

The reactivation of the Hill reaction in CO2-depleted broken chloroplasts by various concentrations of bicarbonate was measured in the absence and in the presence of photosystem II herbicides. It appears that these herbicides decrease the apparent affinity of the thylakoid membrane for bicarbonate. Different characteristics of bicarbonate binding were observed in chloroplasts of triazine-resistant Amaranthus hybridus compared to the triazine-sensitive biotype. It is concluded that photosystem II herbicides, bicarbonate and formate interact with each other in their binding to the Qв-protein and their interference with photosynthetic electron transport.

Fibrinogen binding to the integrin αIIbβ3 modulates store-mediated calcium entry in human platelets

Blood ◽  
2001 ◽  
Vol 97 (9) ◽  
pp. 2648-2656 ◽  
Author(s):  
Juan A. Rosado ◽  
Else M. Y. Meijer ◽  
Karly Hamulyak ◽  
Irena Novakova ◽  
Johan W. M. Heemskerk ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Polymerization ◽  
Adenosine Diphosphate ◽  
Inhibitory Effect ◽  
Human Platelets ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Integrin Αiibβ3 ◽  
Fibrinogen Binding

Abstract Effects of the occupation of integrin αIIbβ3 by fibrinogen on Ca++signaling in fura-2–loaded human platelets were investigated. Adding fibrinogen to washed platelet suspensions inhibited increases in cytosolic [Ca++] concentrations ([Ca++]i) evoked by adenosine diphosphate (ADP) and thrombin in a concentration-dependent manner in the presence of external Ca++ but not in the absence of external Ca++ or in the presence of the nonselective cation channel blocker SKF96365, indicating selective inhibition of Ca++entry. Fibrinogen also inhibited store-mediated Ca++ entry (SMCE) activated after Ca++ store depletion using thapsigargin. The inhibitory effect of fibrinogen was reversed if fibrinogen binding to αIIbβ3 was blocked using RDGS or abciximab and was absent in platelets from patients homozygous for Glanzmann thrombasthenia. Fibrinogen was without effect on SMCE once activated. Activation of SMCE in platelets occurs through conformational coupling between the intracellular stores and the plasma membrane and requires remodeling of the actin cytoskeleton. Fibrinogen inhibited actin polymerization evoked by ADP or thapsigargin in control cells and in cells loaded with the Ca++ chelator dimethyl BAPTA. It also inhibited the translocation of the tyrosine kinase p60src to the cytoskeleton. These results indicate that the binding of fibrinogen to integrin αIIbβ3 inhibits the activation of SMCE in platelets by a mechanism that may involve modulation of the reorganization of the actin cytoskeleton and the cytoskeletal association of p60src. This action may be important in intrinsic negative feedback to prevent the further activation of platelets subjected to low-level stimuli in vivo.

The mechanism of cyclic phosphorylation by illuminated chloroplasts

1963 ◽  
Vol 157 (968) ◽  
pp. 332-345 ◽  
Keyword(s):  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Reducing Power ◽  
Catalytic Amount ◽  
Adenosine Diphosphate ◽  
Hill Reaction ◽  
Hydrogen Transport ◽  
Hydrogen Acceptor ◽  
Light Reaction ◽  
The Hill ◽  
Evolution Of Oxygen

In the reaction discovered by Hill (1937, 1939), chloroplasts isolated from the cell were shown to be capable, upon illumination, of reducing an artificial hydrogen acceptor with the concurrent evolution of oxygen. The ‘Hill reaction’ was regarded as a partial model of the light reaction in photosynthesis where limited reducing power and molecular oxygen arose from the photolysis of water. Attempts to relate this reaction to the photochemical events preceding the dark reduction of carbon dioxide in photosynthesis received their first direct support from the finding of San Pietro & Lang (1958) that nicotinamide adenine dinucleotide phosphate ( NADP )can serve as an effective acceptor of hydrogen in the photochemical reaction when the system is supplemented with a catalytic amount of a soluble protein extracted from leaves. Added significance was given to this finding by the further observation of Amon, Whatley & Allen (1959), that hydrogen transport in the reaction could be coupled to the phosphorylation of adenosine diphosphate { ADP ) to yield adenosine triphosphate { ATP ) concurrently with the reduction of NADP and the production of oxygen in the stoicheiometric proportions: l NADP LL 2 jl ATP /^0 2 . They had previously demonstrated a similar coupling of phosphorylation to hydrogen transport when the artificial reagent, ferricyanide, served as hydrogen acceptor (Arnon, Whatley & Allen 1958). In this work, Amon et al. made the further important observation that hydrogen transport in the ferricyanide reaction is strongly stimulated when phosphorylation occurs concurrently.

Antibodies to Chlorophyll and their Reactions with Chloroplast Preparations

1971 ◽  
Vol 26 (5) ◽  
pp. 435-446 ◽  
Author(s):  
Alfons Radunz ◽  
Georg H. Schmid ◽  
Wilhelm Menke
Keyword(s):  
Photosystem I ◽  
Electron Flow ◽  
Membrane Surface ◽  
Protein Composition ◽  
Inhibitory Effect ◽  
Hill Reaction ◽  
Protein Layer ◽  
Lamellar System ◽  
Light Reaction ◽  
Photosynthetic Electron Flow

Antibodies to chlorophyll are specifically adsorbed onto the membrane surface of thylakoids. The antibodies inhibit photosynthetic electron flow from water to NADP⊕. This inhibition is presumably caused by adsorption of the antibodies onto the centre chlorophyll of light reaction II. Fragments of the thylakoid membrane, obtained by ultrasonication and subsequent fractioning centrifugation, exhibit only photosystem-I activity. Conversely, the specific adsorption of antibodies to sensitizer chlorophyll has no inhibitory effect on electron transport. The ferricyanide Hill reaction of chloroplast preparations is inhibited by chlorophyll antibodies. From these observations it is concluded that the centre chlorophyll of light reaction II and at least part of the sensitizer chlorophyll is located on the surface of the thylakoids. As agglutination is sterically inhibited by the membrane protein, it is assumed that the chlorophyll is located in gaps or pores of the protein layer.Two fractions of the lamellar system exhibit photosystem I activity of different characteristic electron donor specificity. These fractions can be further distinguished in terms of their circular dichroism and protein composition.

Formate as an Inhibitor of Photosynthetic Electron Flow

1984 ◽  
Vol 39 (5) ◽  
pp. 386-388 ◽  
Author(s):  
Jan F. H. Snel ◽  
Dirk Naber ◽  
Jack J. S. van Rensen
Keyword(s):  
Inhibitory Action ◽  
Electron Flow ◽  
Hill Reaction ◽  
Maximal Inhibition ◽  
Photosynthetic Electron Flow ◽  
The Hill

The effects of formate on the Hill reaction in isolated broken pea chloroplasts were in­vestigated. Addition of formate to chloroplasts has two distinct effects: I. basal electron flow can be stimulated 3-fold; 2. uncoupled electron flow is inhibited. The stimulating effect is due to uncoupling by formate and appears instantaneous. Maximal inhibition by form ate is only observed after prolonged illumination. The inhibitory action of form ate on electron flow can be relieved by bicarbonate *.

scholarly journals Functional Characterization of Membrane Sialyltransferase Activity of Human Platelets

1977 ◽  
Author(s):  
K. K. Wu ◽  
C. Ku ◽  
C. Smith
Keyword(s):  
Enzyme Activity ◽  
Functional Characterization ◽  
Adenosine Diphosphate ◽  
Normal Subjects ◽  
Inhibitory Effect ◽  
Human Platelets ◽  
Transferase Activity ◽  
Platelet Surface

To evaluate the role of membrane sialyltransferase in the initiation of platelet aggregation, we studied the stimulatory effect of epinephrine and adenosine diphosphate and the inhibitory effect of aspirin on the platelet surface sialyl transferase activity. The enzyme activity was assayed under optimal conditions as determined previously. The assay mixture consisted of intact washed human platelets, CMP-14C-sialic acid, desialated fetuin, Mn2+ and buffer to a final volume of 1 ml. The enzyme activity was enhanced to 172% of control by 1μH, 152% by 5μM and 146% by 10μM epinephrine. Adenosine diphosphate enhanced the enzyme activity to a lesser extent:103% at 1μM and 113% at 5μM. In contrast, aspirin inhibited the enzyme activity to 46% of control when 10μg/ml of aspirin was used. Higher concentrations of aspirin failed to cause further inhibition. In the in-vivo experiment, 600 mg aspirin was given to normal subjects and the surface enzyme activity was determined 12 hours later. The enzyme activity reduced to 43% following aspirin administration. Furthermore, we studied the enzyme activity in a patient with “aspirin-like” release disorder. While the mean surface enzyme activity of 10 normal subjects was 1.56 + 0.21 (S. D.) pmole-hr-1 per 108 platelets, the enzyme activity of the patient was only 0.91 pmole.hr-l. The results strongly suggest that the membrane sialyltransferase plays an important part in the initiation of platelet release reaction.

Effects of Pyrazon on Growth, Photosynthesis, and Respiration

Weed Science ◽  
1969 ◽  
Vol 17 (3) ◽  
pp. 344-348 ◽  
Author(s):  
R. Frank ◽  
C. M. Switzer
Keyword(s):  
Oxygen Evolution ◽  
Dry Matter ◽  
Structural Integrity ◽  
Inhibitory Effect ◽  
Hill Reaction ◽  
Sugar Beets ◽  
Common Lambsquarters ◽  
Leaf Discs

The herbicide 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) had a ten-fold greater inhibitory effect on the growth of common lambsquarters (Chenopodium album L.) than on sugar beets (Beta vulgaris L.), Production of dry matter was inhibited by accumulations of pyrazon in the tissues. When these accumulations reached a level approximately twice that which affected dry matter production, plants wilted, collapsed, and died. Pyrazon failed to affect the structural integrity of either chlorophyll or the chloroplast, but inhibited the Hill reaction of chloroplasts isolated from both sugar beets and common lambsquarters. The I50 value was 6 × 10−6 M pyrazon. There was no difference between sugar beets and common lambsquarters in the degree of inhibition in oxygen evolution by leaf discs placed in pyrazon. When plants were cultured in vivo with pyrazon, the rate of oxygen evolution was correlated with herbicide accumulations in the leaf tissues. Sugar beet leaves contained only one-third to one-fifth the level present in common lambsquarters. The rates of respiration of roots and leaf discs of both species were not affected by pyrazon treatments in vivo or in vitro.

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