PubMed Health⌕ Search

Biomedical subjects

F Crescitelli

Publications and source records attributed to F Crescitelli.

At least 37 records · Page 2Linked to original sources
PubMed1981

The gecko visual pigment: a pH indicator with a salt effect.

1. Unlike rhodopsin, the extracted 521-pigment of the Tokay gecko (Gekko gekko) is pH-sensitive and changes its spectral absorbance in the pH range of 4.5-7.3. The colour change is reversible and pH can be employed to adjust the spectral maximum anywhere between 490 nm and its native location at 521 nm.2. The hypsochromic shift with increasing acidity is opposite to that expected for the protonation of the Schiff base nitrogen and suggests an action on the secondary system of interacting charges that have long been postulated to adjust vertebrate visual pigment colour within the visible spectrum.3. Chloride ions modulate this pH effect in a systematic and significant manner. For the pigment extracted in the chloride-deficient state the colour change occurs in the pH range of 6.0-7.0, the midpoint being close to 6.5, suggesting the possible participation of the imidazole group of histidine as the functional moiety. With added NaCl the colour shifts to the region below pH 6.2.4. The modulating action of chloride is postulated to be a conformational change of the opsin leading to a shift of the secondary interacting site from one functional group to another or else to a change in pK of a single group due to the conformational alteration of the electrostatics of the system.5. At pH values between 7.5 and 9.0 a different mechanism becomes apparent. In this region a decrease occurs in the photopigment density as well as a shift in absorbance toward the blue. This alkaline effect is readily reversed either by adding NaCl or else by lowering the pH. Along with the other protective effects of chloride these ions serve to reduce or prevent this alkaline loss in density.6. Associated with this reversible photopigment loss is a reversible appearance of a product with a maximum at about 366 nm. The spectrum of this product is like that produced by the addition of 11-cis retinal to the extract. Acidification of the alkaline preparation leads to a restitution of the photopigment as well as to a reduction of the 366-product.7. Addition of hydroxylamine to the alkaline extract in appropriate concentration inhibits the restitution of pigment-521 with acid or NaCl, but adding 11-cis retinal to the system leads to restoration of the photopigment after acidification. All the evidence suggests that product-366 is either free 11-cis retinal or else held to the opsin in a form that does not alter its spectral absorbance. The alkaline effect is therefore a disruption of the aldimine bond of the visual pigment.8. In many respects the gecko 521-pigment behaves like the chicken cone pigment, iodopsin, suggesting that an investigation of the latter in terms of pH may be a worthy project for future study.9. With its ability to change colour with pH, with chloride, with nitrate, etc. the extractable gecko pigment offers possibilities for the investigation of mechanisms responsible for adjusting visual pigment absorbance throughout the visible spectrum. The techniques of circular dichroism, Raman spectroscopy, infra-red spectroscopy, etc. may find here a suitable material for these studies.

Animals↗
PubMed1979

The gecko visual pigments. The behavior of opsin.

The 521-pigment extracted out of the retina of the Tokay gecko has the typical stereospecificity of the vertebrate visual pigments. This is true for the pigment in the chloride-depleted, "blue-shifted" state as well as for the normal pigment with added chloride. While in the chloride-deficient state, pigment regeneration occurred with both 11-cis- and 9-cis-retinals and the regenerated photopigments were also in the blue-shifted, chloride-depleted state. As with the native pigment, these regenerated pigments were bathochromically shifted to their normal positions by the addition of chloride. Chloride-deficient opsin by itself also responded to chloride for the pigment regenerated with 11-cis-retinal from such chloride-treated opsin was in the normal 521-position. Regeneration was always rapid, reaching completion in less than 5 min, and was significantly faster than for cow rhodopsin regenerating under the same conditions. This rapid rate was found with or without chloride, with both 11-cis- and 9-cis-retinals and in the presence of the sulfhydryl poison, p-hydroxymercuribenzoate (PMB). Like the native chloride-deficient pigment, the regenerated chloride-depleted photopigments responded to PMB by a blue shift beyond the position of the chloride-deficient state. The addition of chloride to these "poisoned" regenerated pigments caused a bathochromic shift of such magnitude as to indicate a repair of both the PMB and chloride-deficient blue shift. In this discussion the possible implications of these results to phylogenetic considerations are considered as well as to some molecular properties of the 521-pigment.

Animals↗
PubMed1977

Ionochromic behavior of Grecko visual pigments.

Digitonin extracts of the retina of Gekko gekko prepared to minimize the presence of chloride ions show the photopigment to be at about 490 nanometers rather than at 521 nanometers, the position found for the same pigment in situ. The addition of chloride to the extract causes a bathochromic shift in spectral absorbance, the magnitude of the shift being related to the concentration of chloride, within limits. The effect is a specific one, and of all the anions tested only bromide causes a similar bathochromic shift. The nature of the cation is not involved since the same action is produced by the chlorides of sodium, lithium, potassium, rubidium, cesium, calcium, magnesium, beryllium, lanthanum, and choline.

Animals↗
PubMed1977

The gecko visual pigments: a microspectrophotometric study.

1. A dual system of visual pigments having absorbance maxima in the green and blue respectively has been found in the retinas of geckos both by single cell microspectrophotometry and by the method of extraction. Microspectrophotometry has shown the system to be present in four species of geckos representing four genera. Along with previous work with extracts (Crescitelli, 1972) this indicates a fundamental property in this family of lizards. No other photopigments have been detected.2. For Gekko gekko, the species most intensively studied, the two pigments have absorbance maxima at 521 and 467 nm respectively. Both are based on vitamin A(1) and both are characterized by absorbance spectra that nearly conform to the Dartnall nomogram.3. In situ, the 521-pigment is not temperature-sensitive, and has virtually the same absorbance spectrum at 23 degrees C as at 5 degrees C. On extraction into digitonin solution, however, the absorbance spectrum of the pigment becomes temperature-dependent and, though identical when measured at low temperature (2-5 degrees C) with the constant in situ curve, is displaced to shorter wave-lengths at higher temperatures (10-25 degrees C). Thus the extract spectrum is relevant to the in situ spectrum only at low temperature (and in the presence of chloride ions).4. Unlike the rhodopsins of several vertebrates, the gecko 521-pigment displays no evidence of a meta-III stage in the sequence of products following photic bleaching, even at low temperatures. This is true for the pigment in situ as well as in the extracted condition.

Animals↗