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S Demeter

Publications and source records attributed to S Demeter.

12 recordsLinked to original sources
PubMed1992

Thermoluminescence evidence for light-induced oxidation of tyrosine and histidine residues in manganese-depleted photosystem II particles.

In the thermoluminescence (TL) glow curve of photosystem II, particles depleted of manganese, a tyrosine modifier, 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD) abolishes the TL band appearing around -55 degrees C (TL-55). Addition of a histidine modifier, diethylpyrocarbonate results in the disappearance of the band peaking around -30 degrees C (TL-30). NBD treatment also abolishes the EPR signal IIfast of oxidized tyrosine donor, Yz, and inhibits the electron transport from diphenylcarbazide to 2,6-dichlorophenol-indophenol. It is concluded that the TL-55 and TL-30 bands can be assigned to oxidized tyrosine (Yz+) and histidine (His+) residues, respectively, which participate in electron transfer from manganese to the reaction center of chlorophyll, P680+.

4-Chloro-7-nitrobenzofurazan↗
PubMed1991

Bi-versus monohemispheric performance in split-brain and partially split-brain macaques.

Experiments comparing binocular with monocular abilities of monkeys working on visual mnemonic tasks were performed. First, it was shown that even in split-brain monkeys performance was more accurate when both hemispheres were utilized than when the task was performed with only the single (better) hemisphere. Some form of noncommissural integration is thus possible. However, when the forebrain commissures are present, as in four other animals (with only optic chiasm transected) it was shown that integration occurs via callosal mechanisms as well. This was demonstrated by the fact that here, too, binocular performance was normally more accurate than monocular performance, but when different images to be remembered were presented concurrently to the two eyes, the binocular advantage was lost. Finally, in three monkeys with only the anterior commissure allowing interhemispheric communication the superiority of binocular assessment remained even when the two hemispheres simultaneously received such differing images.

Animals↗
PubMed1990

Fields of origin and pathways of the interhemispheric commissures in the temporal lobe of macaques.

The interhemispheric connections of the cortical areas of the temporal lobe and some neighboring regions were investigated in monkeys (Macaca mulatta and Macaca fascicularis) by anterograde autoradiographic tracing, following injection of radioactively labeled amino acids. The results revealed that the interhemispheric projections of the temporal lobe course through three interhemispheric commissures on their way to the opposite hemisphere. The anterior commissure receives fibers from virtually the entire temporal lobe, including the temporal pole, superior and inferior temporal gyri, and parahippocampal gyrus. Moreover, area 13 of the orbitofrontal cortex, the frontal and temporal subdivisions of the prepiriform cortex, and the cortical and deep nuclei of the amygdala also contribute fibers to the anterior commissure. The heaviest projections arise in the rostral third of the temporal isocortex. These projections become progressively lighter from more caudal regions. By contrast, the corpus callosum receives fibers from the caudal two-thirds of the temporal lobe, including the temporal pole, superior and inferior temporal gyri, and parahippocampal gyrus. The heaviest projections arise in the caudal third of the temporal lobe and cross primarily in the caudal third of the corpus callosum, including the splenium. Progressively lighter projections arise more rostrally. Fibers from proisocortical and isocortical areas of the posterior parahippocampal gyrus cross in the ventralmost part of the splenium (inferior forceps), whereas cortical areas lateral to the occipitotemporal sulcus give rise to fibers that cross in the caudal part of the body of the corpus callosum and dorsal splenium. The dorsal hippocampal commissure receives fibers exclusively from the parahippocampal gyrus. The fibers of the corpus callosum, hippocampal commissure, and, to a lesser extent, the anterior commissure are intimately associated with the ventricular system as they course through the white matter of the temporal lobe. The fields of origin of the anterior commissure and corpus callosum overlap extensively over the caudal two-thirds of the temporal lobe. The posterior parahippocampal gyrus is unique in that it gives rise to fibers that cross in all three commissures.

Amygdala↗
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↗
PubMed1990

Multiplane gallium tomography in assessment of occupational chest diseases.

Gallium-67 scintigraphy is helpful in the evaluation of inflammatory, respiratory diseases. Single-photon emission computed tomography (SPECT) provides three-dimensional tomographic reconstruction of radioisotope distribution in the body. The addition of SPECT to gallium-67 scanning in 27 patients demonstrated an improvement in the sensitivity for detecting the presence and extent of interstitial occupational lung disease. This technique may provide earlier detection of parenchymal lung changes than can the chest x-ray and planar scanning in some patients with asbestosis. Findings in six patients with asbestosis are reported.

Adult↗
PubMed1977

Electrochemical and spectro-kinetic evidence for an intermediate electron acceptor in photosystem I.

Absorption changes accompanying light-induced P-700 formation and its decay in the dark at 15 K in Photosystem-I particles poised at various redox potentials have been examined. In unpoised samples, the light-induced absorption change is practically irreversible. At increasingly negative potentials, an increasing fraction of the absorption change, proportional to the fraction of bound iron-sulfur protein chemically reduced, becomes reversible, and the titration curve has a midpoint potential of --530 mV (vs. normal hydrogen electrode). At --66 mV, the P-700 absorption change is 97% reversible. The total P-700-signal amplitude decreases over the same potential span and levels off at about 43% (to slightly over 50% at a substantially higher excitation intensity). These results provide additional support to previous suggestions of an existence of an intermediate electron acceptor located between the primary donor, P-700, and the more stable primary electron acceptor (P-430 or bound iron-sulfur protein).

Electrochemistry↗
PubMed1976

The development of the intense circular-dichroic signal during granum formation in greening etiolated maize.

In greening maize mesophyll, circular dichroism (c.d.) revealed the early formation of protein-chlorophyll complexes, followed by unorganized chlorophyll. The intense c.d. [Gregory & Raps (1974) Biochem. J. 142, 193-201] appeared later still, whereas membrane-membrane contact (stacking), measured from electron micrographs, appeared much earlier. Isolated grana, which still showed stacking, lost 92% of their original intense c.d.; intense c.d. is not therefore simply dependent on stacking.

Chloroplasts↗
PubMedDate not supplied

Prevalence of HBeAg and anti-HBe in blood donors with HBs antigenemia.

250 HBsAg-positive sera from apparently healthy blood donors were tested for HBeAg and anti-HBe by immunodiffusion(ID) and counterelectrophoresis(CEP). HBeAg was identified in 2.4% and anti-HBe in 34% of the sera. After serum concentration a larger rate of both HBeAg and anti-HBe could be detected by ID. There was no difference in sensitivity between ID and CEP techniques in the detection of the e-system. There was no correlation between HBeAg or anti-HBe and HBsAg subtypes. Generally sera containing HBeAg showed higher titers of HBsAg in complement fixation.

Antibodies, Viral↗