The endoparasitic helminth communities of the European eel, Anguilla anguilla (L.), were investigated in four meanders, cut off from the rivers Leie and Scheldt in western Handers, Belgium. Six species of helminths (2 cestodes, 2 nematodes and 2 acanthocephalans) were found. The dominant parasite species was the nematode Anguillicola crassus (Kuwahara, Niimi et Itagaki, 1974) infecting 79% of the eel population with intensities up to 112 specimens per fish. At two localities no acanthocephalans could be found, whereas these parasites were very common at the other sites. The prevalence, mean intensity, intensity and abundance, their correlation to the body length, and the frequency distributions were analysed. The site selection of parasites is in relation to food composition and feeding habits of eels, physiological and structural differences in the intestine and possible interspecific competition were discussed.
The formation of S-aminolevulmic acid (ALA), energy-dependent steps ffom ALA to protoporphyrin IX (Proto) and from Proto to protochlorophyllide (PChlide) formation, the roles of NADPH in PChlide photoreduction and geranylgeraniol hydrogenation, the source of adenylates and reduced pyridine nucleotides for the reactions of chlorophyll biosynthesis, and the compartmentation and interrelationships of porphyrin biosynthesis pathways are reviewed.
The pH-dependent quenching of chlorophyll (Chl) fluorescence (the high energy quenching) was characterized by stationary Chl-a-fluorescence in the thylakoid membranes and photosystem (PS) 2 preparations. The variable part of fluorescence was quenched, when the pH in the thylakoid lumen decreased below 5.5, i.e., at high ApH. This quenching was caused by an inhibition of electron donation from the manganese cluster to the reaction centre of PS 2. The pH response of quenching suggested that a 1 H'''-transition with an apparent pK of 4.7 was involved. Parallel to quenching at low pH, a Ca^‘'‘-release was measured (1 Ca^'*' per 200 Chl). When the ApH relaxed and the pH on the lumen side increased again, fluorescence recovered provided Ca^'*' was present (Kd = 100 pM). Both the quenching at low pH and the reactivation at pH > 5.5 are light-dependent processes. In the presence of high concentration of extemal Ca^"^, fluorescence recovered even at low pH. Inhibition of the donor-side of PS 2 directly affected the acceptor-side of PS 2, as seen by a shift of the redox potential of Qa from -120 mV (pH 7.0) to +40 mV (pH 4.2). We propose that at high ApH (7) the water splitting side is inactivated by release of Ca from a high afflnity binding site, and (2) Qa is converted to a high-potential form. Excitatíon energy is then dissipated at the PS 2 reaction centres by a recombination reaction between donor and acceptor side. As a result, Qa (and the intersystem electron transport chain) remains oxidized, even in the excessive light.
Článek se nejprve zabývá formálními rysy kompozit, a sice jejich pravopisem a otázkami polohy přízvuku. Jelikož se však na základě formálních kritérií nedojde obvykle к uspokojivému vysvětlení podstaty kompozit, hledá se řešení v oblasti sémantiky. Hlavní část této menší studie si klade za cíl přispět к výkladu z pohledu psycholingvistiky. Na anglická kompozita je totiž možno pohlížet jako na minimální idiomatické výrazy, které v závislosti na kontextu mohou mít doslovnou i figurativní významovou interpretaci a které jsou charakterizovány gramatickou a lexikální invariabilitou. Jsou tedy kompozita spojeními nekompozicionálními, kde celkový význam v pohledu synchronním je vzdálen prosté komputaci významů jejich složek. Postulovaná nekompozicionálnost není však totéž jako nepředvídatelnost významu, což je na mnohých příkladech ilustrováno. Důležité je rovněž zjištění, že v každém okamžiku existence jazyka nalézáme spojení, která jakoby hraničí s volnými kombinacemi a mohou se stát "kandidáty" pravých kompozit, právě v závislosti na kontinuálně se snižujícím stupni kompozicionálnosti.
On February 20 of this year, 70 years passed since the death of the traveller, writer, photographer, collectioner and adventurer in the best sense of the word - Enrique Stanko Vráz. His origin and youth have been up to now covered with doubts. The first documents relate only to the first journey of Vráz outside Europe. Since 1880, Vráz lived in Africa - in Marocco, Gambia and on the Gold Coast (modern Ghana), where he started to photograph. After a short stay on the Canary Islands he headed for South America and decided to transverse it in the equatorian part. This goal he completed successfully. After this, he travelled between America and Europe, he visited Japan, New Guinea, Thailand, China, Korea, Siberia. Then he again started for South America and for Mexico. During all his trips Vráz made photos. Some of his photographs, preserved today in the Náprstek Museum, are absolutely unique. Vráz perceived photography as a natural media for documentation, he placed its informative value above the emotional. The most frequent topics of his photographs were architecture and its details, nature, landscape and especialy the recordings of the everyday life. These photos have a high documentary value because of the place and the time of origin and also because of the fact that Enrique Stanko Vráz was a sensitive observer that wanted to utilize the photography to informe about the life in the distant, strange lands.
We determined the surface-associated proteolytic activity in three Entamoeba histolytica Schaudinn, 1903 strains (monoxenic HM1, axenic HM1, and HK9) of known virulence and its relationship with collagenase activity. Both activities were also determined in axenic HM1 amoebae trophozoites which were sensitive and resistant to complement-mediated lysis. Surface proteolytic activity was determined in glutaraldehyde-fixcd E. histolytica trophozoites, which degraded the insoluble substrate, hide powder azure, and cleaved the human immunoglobulin G heavy chain in a time-dependent fashion, at neutral pH, in presence of 2-mercaptoethanol as cysteine protcase activator. Surface proteolytic activity was strain dependent: monoxenic HM1 > axenic IIM1 > axenic HK9. This activity correlated with collagenolytic activity (p < 0.05). Acquisition of resistance to complement-mediated lysis by axenic HM1 strain did not modify either surface proteases or collagenase expression. Our results suggest that this surface proteolytic activity could be used as an in vitro virulence marker for E. histolytica.