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V Passarelli

Publications and source records attributed to V Passarelli.

10 recordsLinked to original sources
PubMed2000

The photoreceptor protein of Euglena gracilis.

We isolated the photoactive protein Erh, isolated from the photoreceptor of the unicellular photosynthetic flagellate Euglena gracilis. It is a 27 kDa protein with a photocycle resembling that of sensory rhodopsin, but with at least one stable intermediate. We recorded the absorption spectrum of the parent form of this protein both under native form and in the presence of hydroxylamine and sodium borohydride, and the fluorescence spectra of both the parent and intermediate forms. We suggest that Erh is a rhodopsin-like protein and propose a simple photocycle. This protein shows optical bistability, without thermal deactivation.

Animals↗
PubMed2000

Ultrastructure of the pellicle of Euglena gracilis.

Deep-etching technique was used to investigate the organization of the pellicle complex of Euglena gracilis. The interpretation of the images was further supported by SEM and TEM investigations. Our results mainly validate data obtained by previous freeze-fracture studies on the E and P faces of the outer cortical membrane. At the level of the ridges, the outer E fracture face is highly organized in a regular striated pattern, whereas the P inner face shows a particulate structure. However, our images reveal that this particulate organization of the P face is not limited to the ridges, but it is displayed also by the grooves. Moreover, this face shows two distinct layers, a particulate layer facing the cytoplasm and a striated layer facing the E face; these layers represent different true fracture levels of the same P face.

Animals↗
PubMed2000

A complex photoreceptive structure in the cyanobacterium Leptolyngbya sp.

Among the terrestrial epilithic cyanobacteria isolated from Roman hypogea at extremely low light intensity, a non-heterocystous strain, belonging to the genus Leptolyngbya, showed a marked photobehavior. These red cyanobacteria possess an orange spot at the tip of the apical cell. Micro-spectrophotometric analysis of this tip showed an absorption spectrum with two bands, centered at 456 and 504 nm, respectively. Experiments on photo-orientation impairment of these cells, and micro-spectrophotometric analysis of the tip of impaired trichomes showed that a rhodopsin-like protein might be present in this structure. All these data could support the hypothesis of the presence of a complex photoreceptive system in this prokaryote.

Bacterial Proteins↗
PubMed1997

In vivo photocycle of the Euglena gracilis photoreceptor.

We present the light-induced photocycle of the paraflagellar swelling of Euglena gracilis. The kinetics of this process was reconstructed by sampling its fluorescence emission and switching the excitation light from 365 nm to 436 nm. Stable intermediates in the photocycle were manifested. The measured millisecond resolution kinetics best fits a Michaelis-Menten equation. The data provide strong evidence that the paraflagellar swelling, a three-dimensional natural crystal of a light-detecting protein, is the true Euglena photoreceptor.

Animals↗
PubMed1993

Effects of hydroxylamine, digitonin and triton X-100 on photoreceptor (paraflagellar swelling) and photoreception of Euglena gracilis.

We present experiments that test the effects of agents commonly used in visual pigment investigations, namely hydroxylamine (NH2OH), digitonin and triton X-100, on the photoreceptor and photoreception of Euglena. Hydroxylamine reacts with free and opsin-bound retinal, in aqueous solution, to form stable oximes, whereas digitonin and triton X-100 are the most common extractants of rhodopsin. Since previous data indicate that the chromophore present in Euglena photoreceptor is retinal, we investigated the influence of these chemicals on this organelle. The effects of these agents were studied by means of phase contrast, fluorescence and transmission electron microscopy and photobehaviour experiments. Hydroxylamine inhibited the formation of the Euglena photoreceptor. Photoaccumulation experiments on hydroxylamine-treated cells showed that they are unable to perceive light. Digitonin solubilized the crystalline structure of the photoreceptor, whereas the triton effect was limited to the membranous structures of the cell, leaving the photoreceptor unimpaired.

Animals↗
PubMed1992

Identification of a rhodopsin photoreceptor in Euglena gracilis.

Visual pigments are a class of receptor proteins that absorb light and trigger sensory signals. Retinal-containing proteins are used in nature as photoreceptors mainly in animals vision. Mammalian rhodopsin is the best studied example of a light sensor which couples photon absorption to a cascade of biochemical reactions amplifying the input signal. A surprising discovery was to find rhodopsin also in Archaebacteria and in unicellular eukaryotes. On the basis of absorption microspectroscopic measurements and of inhibition experiments on pigment biosynthetic pathways, we have recently suggested that a rhodopsin could be the functional receptor of the visual process in Euglena gracilis, a flagellate which can use light directly to promote photosynthetic reactions, or as an incident flux of information to adjust its swimming orientation. We here report purification and identification of all-trans-retinal by column chromatography, HPLC and GC-MS in E. gracilis; these findings indicate with absolute certainty that rhodopsin is the photoreceptor molecule of this microorganism.

Animals↗
PubMed1991

Ultrastructure of the apical zone of Euglena gracilis: photoreceptors and motor apparatus.

Euglena is an organism that every student of biology has observed; its morphology has been a subject of interest since the early microscopic literature for its enigmatic role of "plant-like" or "animal-like" organism. Therefore, this review has no pretensions to absolute novelty, but, like a journey to the centre of the earth, will attempt to arouse the reader's curiosity by taking him inside the cell Euglena, through the canal opening into the reservoir chamber. In light of the most recent knowledge, though much remains to be clarified, the aim is to provide information from ultramicroscopical studies on the apical zone of Euglena and possible functional meanings of the structures present therein. The survey of these structures is carried on as a study in correlation: TEM of cells after various treatments is correlated with SEM of cells fixed by means of different techniques. Notes on locomotion and other features of cytological and biological interest are added to assist with the comprehension of this microorganism.

Animals↗
PubMed1988

Microorganism track reconstruction: an image processing approach.

This paper presents an automatic system for the analysis of microorganism behaviour. The movements of free swimming microorganisms are videotaped by means of a television camera mounted on a microscope. The analysis is performed off-line by digitizing the video signal through the use of an image processor unit. Microorganism tracks are reconstructed spatially and chronologically by means of image processing techniques. From these tracks cell movement parameters are obtained. The results of our experiment in testing photoinduced movements follow.

Algorithms↗
PubMedDate not supplied

Chitosan as flocculant for concentrating Euglena gracilis cultures.

The practical criteria for the usefulness of an algal separation process for laboratory routine being effectiveness and time consumption, we tested the feasibility of a flocculation procedure to harvest large volumes of Euglena gracilis in culture. This procedure turned out to be a technically viable system which avoided tedious centrifugation and preserved E. gracilis flagellar apparatus integrity. E. gracilis cultures were treated with chitosan, a by-product derived from chitin from the exoskeleton of crustaceans. Since this polymer carries a positive charge, it functions as a polycationic coagulating agent by adsorbing onto particles in suspension and by bridging together into agglomerates, or flocs. A 96-98% reduction of suspended cells in cultures with 200 mg/l of chitosan, at pH 7.5, was obtained.

Animals↗