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At least 595 records · Page 33Linked to original sources
PubMed1991

Interaction between casein and vitamin A during food processing.

A particular relation exists between casein micelle and vitamin A. In vitro, large amounts of retinol are fixed to acid casein and its different fractions by hydrophobic bindings. The binding on the hydrophobic amino-acid residues (Trp, Phe) is greatly facilitated by a configurational change in the molecule exposed to physico-chemical parameters: alcalinity and heat treatments. Another amount of retinol is even more strongly fixed by a binding which can only be broken by saponification. Casein plays an important role in stabilizing retinol which does not degrade over time or during heat treatments. In vivo, when the retinol availability is measured by the vitamin A content in the liver, acid casein somewhat increases the retinol efficiency and, even more so, the retinal efficiency. Nevertheless, this favourable action is only observed under particular conditions: balanced diet, casein from milk, etc. For the moment, the animal data cannot be directly linked with the properties of binding appearing in vitro.

Animals↗
PubMed1990

Electrophysiologic characteristics of human and rat retinas in vitro.

To promote studies on the human retina, we investigated the survival of function in postmortem specimens. Visual pigment has been regenerated in normal human retinas, 5 to 58 hours postmortem, by exposure to retinal isomers in the dark. Levels from 0.1 to 0.41 nmol/mg protein were reached. Photoresponses were obtained in 9 of 13 retinas: P III maximum amplitudes ranged from 20-398 microV and thresholds, taking the criterion amplitude as 3 microV, ranged from 8.8-1340 quanta/micros2. In three cases, the b-wave was also seen. The P III amplitude vs. log intensity curves gave values of n between 0.6 and 1.0, and sigma (the stimulus intensity for a half maximal response) between 132-3700 quanta/microns2. Recovery of sensitivity did not always correspond to that of maximum response.

Adolescent↗
PubMed1981

Linear analysis of the responses of simple cells in the cat visual cortex.

Spatial response profiles to stationary and moving stimuli and spatial frequency tuning curves to drifting sinusoidal gratings were recorded from a series of cells in the simple family. The spatial response profiles were recorded both to stationary flashing bars and sinusoidal gratings as well as to light and dark bars and edges and gratings moving at the optimal velocity. On the assumption that cells in the simple family operate linearly, spatial response profiles recorded experimentally were compared with those predicted by inverse Fourier transformation of the spatial frequency tuning curves. Conversely, the spatial frequency tuning curves recorded experimentally were compared with those predicted from the response profiles to moving and stationary stimuli. As a result of these comparisons, it is clear that moving stimuli provide a more accurate estimate of the spatial organization of the receptive field than do stationary stimuli. Cells with the higher optimal spatial frequencies tended to have narrower bandwidths. The simple cell with the narrowest bandwidth (0.94 octave) had five, and possibly six, subregions in the spatial response profile to moving light and dark bars, the largest number of subregions we encountered.

Animals↗
PubMed1994

The archaebacterial membrane protein bacterio-opsin is expressed and N-terminally processed in the yeast Saccharomyces cerevisiae.

The bop gene codes for the membrane protein bacterio-opsin (BO), which on binding all-trans-retinal, constitutes the light-driven proton pump bacteriorhodopsin (BR) in the archaebacterium Halobacterium salinarium. This gene was cloned in a yeast multi-copy vector and expressed in Saccharomyces cerevisiae under the control of the constitutive ADH1 promoter. Both the authentic gene and a modified form lacking the precursor sequence were expressed in yeast. Both proteins are incorporated into the membrane in S. cerevisiae. The presequence is thus not required for membrane targeting and insertion of the archaebacterial protein in budding yeast, or in the fission yeast Schizosaccharomyces pombe, as has been shown previously. However, in contrast to S. pombe transformants, which take on a reddish colour when all-trans-retinal is added to the culture medium as a result of the in vivo regeneration of the pigment, S. cerevisiae cells expressing BO do not take on a red colour. The precursor of BO is processed to a protein identical in size to the mature BO found in the purple membrane of Halobacterium. The efficiency of processing in S. cerevisiae is dependent on growth phase, as well as on the composition of the medium and on the strain used. The efficiency of processing of BR is reduced in S. pombe and in a retinal-deficient strain of H. salinarium, when retinal is present in the medium.

Alcohol Dehydrogenase↗
PubMed1991

Photoreceptor differentiation in cerebellar medulloblastoma: evidence for a functional photopigment and authentic S-antigen (arrestin).

The aim of the present study was to evaluate the putative photoreceptor differentiation found in certain cerebellar medulloblastomas. The analyses were focussed on S-antigen, rod-opsin (the apoprotein of the visual pigment rhodopsin) and 11-cis retinal (the prosthetic group of rhodopsin). Fresh frozen and paraffin-embedded biopsy specimens of three medulloblastomas were investigated by means of immunocytochemistry, enzyme-linked immunosorbent assay (ELISA), high-pressure liquid chromatography (HPLC), and immunoblotting. As shown in paraffin sections, one out of the three tumors (tumor A) contained S-antigen- and rod-opsin-immunoreactive tumor cells. The immunoblotting technique revealed in this tumor a single protein band of approximately 48-50 kDa that reacted with the S-antigen antibody and three protein bands of approximately 40, 75 and 110 kDa recognized by the rod-opsin antibody. These bands could not be detected in the two remaining tumors (tumor B and C). The rod-opsin content of tumor A was quantified by the ELISA; 11.7 pmol rod-opsin were calculated for the biopsy. The HPLC demonstrated the presence of 11-cis- and all-trans-retinal in tumor A, but not in tumors B and C. Furthermore, it was shown that 11-cis-retinal was converted to all-trans-retinal upon illumination of the tumor extract. The ratio between 11-cis- and all-trans-retinal was approximately 1:1 before illumination and 3:5 after illumination. A total of 2-3 pmol of retinal was found in the biopsy of tumor A. In addition all-trans-retinol was present in this tumor. The results indicate that certain medulloblastomas express a functional photopigment and S-antigen, another protein of the phototransduction cascade. They strongly support the concept that medulloblastoma cells may differentiate along the photoreceptor cell lineage.

Antigens↗
PubMed1989

Comparative distribution, pharmacokinetics and placental permeabilities of all-trans-retinoic acid, 13-cis-retinoic acid, all-trans-4-oxo-retinoic acid, retinyl acetate and 9-cis-retinal in hamsters.

Pregnant hamsters were given a single oral dose (35 mumol/kg) of all-trans-retinoic acid, 13-cis-retinoic acid, all-trans-4-oxo-retinoic acid, 9-cis-retinal or all-trans-retinyl acetate during the early primitive streak stage of development. The radioactivity associated with the acidic retinoids was distributed to all tissues sampled (including placenta and fetus), with the largest accumulation in the liver and the least accumulation in fat. Radioactivity from 9-cis-retinal or retinyl acetate concentrated in the liver and lung. The all-trans-retinoic acid was oxidized in vivo to all-trans-4-oxo-retinoic acid and isomerized to 13-cis-retinoic acid: 13-cis-retinoic acid was oxidized to 13-cis-4-oxo-retinoic acid and isomerized to all-trans-retinoic acid. No parent 9-cis-retinal or retinyl acetate could be detected in maternal plasma. Plasma concentrations of the parent acidic retinoids reached their maxima within 60 min and then followed exponential decay. Of all the retinoids examined here, 13-cis-retinoic acid showed the largest area under the plasma curve, the slowest clearance and the longest elimination t1/2. Total plasma radioactivity, consisting of unidentified metabolites, remained elevated at 4 days after dosing. Maternal peak circulating concentrations of the parent retinoids, total radioactivity, plasma pharmacokinetic parameters or the total concentrations of residual radioactivity in fetal tissues could not be correlated with the differential teratogenic potencies of these retinoids.

Animals↗
PubMed1993

Rod-opsin immunoreaction in the pineal organ of the pigmented mouse does not indicate the presence of a functional photopigment.

The aim of the present study was to characterize the rod-opsin immunoreaction in the mammalian pineal organ. Pigmented mice (strain C57BL) were selected as the animal model. Immunocytochemical investigations involving the use of highly specific polyclonal and monoclonal antibodies against bovine rod-opsin (the apoprotein of the photopigment rhodopsin) showed that approximately 25% of all pinealocytes were rod-opsin immunoreactive. Immunoblotting techniques revealed three protein bands of approximately 40, 75, and 110 kDa; these were detected by the monoclonal antibody and the polyclonal antiserum in retinal and pineal extracts. These protein bands presumably represented the monomeric, dimeric and trimeric forms of rod-opsin. The amount of rod-opsin in retina and pineal organ was quantified by means of an enzyme-linked immunosorbent assay. This yielded 570 +/- 30 pmoles rod-opsin per eye and 0.3 +/- 0.05 pmoles rod-opsin per pineal organ. High pressure liquid chromatography analysis of whole eye extracts demonstrated the chromophoric group of the photopigment rhodopsin, 11-cis retinal, and its isomer, all-trans-retinal. A shift from 11-cis retinal to all-trans-retinal was found upon light adaptation. No retinals were detected in the pineal organ. Autoradiographic investigations showed that 3H-retinol, intraperitoneally injected into the animals, was incorporated into the outer and inner segments of retinal photoreceptors, but not into the pineal organ. It is concluded that the mouse pineal organ contains the authentic apoprotein of rhodopsin but that it lacks retinal derivatives as essential components of all known vertebrate photopigments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1980

Body movements and retinal pattern displacements while approaching a stationary object in the walking fly, Calliphora erythrocephala.

When a walking fly approaches a stationary object two types of body movements are distinguishable. Type I body movements are characterized by low frequencies (0.4-1.3 Hz) and large amplitudes (28-65 degrees). Superimposed on these movements are type II body movements which are characterized by high frequencies (7.3-10.6 Hz) and small amplitudes (5.9-8.2 degrees) (Figs. 3-6; Table 1). Type II movements occur no matter whether the fly is fixating a pattern or orientating itself in homogeneous surroundings without any pattern. In contrast, only 72% of the flies with immobilized heads and 62% of the flies with movable heads make type I body movements. The amplitude of type I and type II body movements increases slightly after immobilization of the head. Binocular as well as monocular pattern projection occurs for the whole walking trajectory (Fig. 7-9). Monocular pattern projection seems to be more frequent in flies with immobilized heads than in those with movable heads. The degree of pattern fluctuations in the visual field of the flies increases slightly along the walking trajectory. Near the starting point in the centre of the arena it amounts to 5-7 degrees, while at the end of the walking trajectory it amounts to 8-10 degrees (Table 2). The following conclusions and hypothesis can be drawn from these experiments. 1. The graph BT for the direction of the fly's longitudinal axis can be approximated by the first derivative of the walking trajectory WT, that means, dWT(x)dx approximately BT(x) (Fig. 11) 2. The amplitudes of type II body movements are caused by the alternating movements of the legs during forward motion, while type I body movements are classified as exploring movements. During evolution of visually guided behaviour it is possible that blowflies have adapted their elementary movement detector system to type II body movements. 3. The types of pattern projection into the visual field of the fly while approaching an object can be explained by a simple neuronal network characterized by either inhibitory and/or excitatory influences of the visually activated neurones on the motor neurones generating the propulsive forces, that means the forward motion. In addition it is postulated that the large frontal and antero-lateral receptive fields of these neurones are not coupled with the motor centres on the same side of the body (Fig 12).

Animals↗
PubMed1976

Evidence for chromophore-chromophore interactions in the purple membrane from reconstitution experiments of the chromophore-free membrane.

We recently presented evidence showing that the visible CD spectrum of the purple membrane from Halobacterium halobium consists of two contributions: a broad positive band centered at the absorption maximum due to the interaction of the chromophore with the protein to which it is bound, and an exciton coupling band due to the interaction between chromophores of adjacent bacteriohodopsin molecules in the hexagonal surface lattice (Heyn et al., 1975); This interpretation receives strong support from the present experiments in which the chromophore-free membrane is reconstituted by the addition of retinal. Since the coupling signal arises from the interaction between pairs of neighboring chromophores, its contribution to the spectrum would be expected to be very small in the initial stages of the titration experiment, but increasing quadratically with the percentage reconstitution. The broad positive band, on the other hand, is expected to increase linearly with the percentage reconstitution. On the basis of these considerations a satisfactory explanation of the CD reconstitution experiments could be given. Since it appears to be impossible to explain the titration experiments without the quadratic term, we conclude that chromophore-chromophore interactions play an important role. No significant changes in secondary structure upon reconstitution should be detected consistent with our binding model which neglects cooperativity;

Bacteriorhodopsins↗
PubMed1980

Photosensory retinal pigments in Halobacterium halobium.

In Halobacterium halobium, nicotine is known to block the synthesis of retinal. Cells grown in the presence of nicotine do not show any photophobic response. Addition of retinal1 or retinal2 restored the photophobic responses to light-increase in the UV and to light-decrease in the green-yellow part of the spectrum. The action spectra of the two retinal2-photosystems were red-shifted by 15--20 nm, compared with the corresponding retinal1 systems. We conclude that each of the two photosystems PS 370 and PS 565, has its own photosensory pigment with retinal as the chromophoric group.

Animals↗
PubMed1979

Interaction of bovine rhodopsin with calcium ions. I: the metarhodopsin I--II reaction and the regeneration of rhodopsin.

The formation of metarhodopsin II in various bovine rhodopsin preparations (rod outer segment (ROS) suspensions and rhodopsin-detergent solutions) was measured by means of flash spectrophotometry. The half-lifetime and formation of metarhodopsin II in ROS did not depend on the calcium concentration in the range of less than 10(-9) M (using EGTA ro EDTA) to 15 x 10(-3) M calcium at pH values of 5.0, 7.1, and 9.0 (Table 1). The regeneration of rhodopsin from opsin by adding 11-cis retinal to ROS-suspensions and rhodopsin digitonin solutions was measured spectrophotometrically. It was not substantially different in either saline, one containing less than 10(-7) M calcium (by adding EGTA), the other containing 10(-3) M calcium (Table 2).

Animals↗
PubMed1979

Molecular mechanism for the initial process of visual excitation. III. Theoretical studies of optical spectra and conformations of chromophores in visual pigments, their analogues and intermdiates based on the torsion model.

The torsion model with which we proposed to interpret the specific properties of the photoisomerization reaction of rhodopsin has been developed to apply to isorhodopsin I, isorhodopsin II and some intermediates. Based on this model, optical absorption wavelengths and oscillator strengths, as well as rotational strengths of visual pigments, analogues and intermediates at low temperatures are analyzed by varying twisted conformations of the chromophores. As a result, it was found that most of the optical data could be very well accounted for quantitatively by the torsion model. The twisting characters in the chromophore of rhodopsin are very similar to those of isorhodopsin. The obtained conformations of the chromophores are very similar in rhodopsin and its analogues, and in isorhodopsin and its analogues. Those of the chromophores of bathorhodopsin, lumirhodopsin and metarhodopsin I are similar to one another except that the conjugated chain of metarhodopsin I bends considerably when compared with the other intermediates.

Animals↗