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At least 667 records · Page 37Linked to original sources
PubMed1979

Resonance Raman study of the dark-adapted form of the purple membrane protein.

The resonance Raman spectrum of the dark-adapted form of the purple membrane protein (bacteriorhodopsin) has been obtained and is compared to the light-adapted pigment and model chromophore spectra. As in the light-adapted form, the chromophore-protein linkage is found to be a protonated Schiff base. Electron delocalization appears to play the dominant role in color regulation. The dark-adapted spectrum indicates a conformation closer to 13-cis than the light-adapted spectrum.

Bacteriorhodopsins↗
PubMed1983

Retinal inhibits TPA activated, calcium-dependent, phospholipid-dependent protein kinase ("C" kinase).

RAW264 macrophage-like cells contain a kinase which is dependent on Ca++ and phosphatidylserine for activity (C kinase) and is stimulable by the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate. Retinal inhibits the activity of the tumor promoter-activated kinase in a concentration-dependent manner. The apparent Ki for inhibition is 1 X 10(-5)M. Retinal is not a general inhibitor of phosphotransferase reactions as it did not inhibit the activity of purified cyclic AMP-dependent protein kinase. It is possible, therefore, that the action of retinoids to antagonize tumor promoter effects on cell function may be mediated at the level of regulation of C-kinase.

Calcium↗
PubMed1983

Evidence for a carboxyl group in the vicinity of the retinal chromophore of bacteriorhodopsin.

Carboxyl groups of bacteriorhodopsin in purple membranes were activated using a hydrophobic reagent and then covalently labeled with a pH-sensitive reporter group, nitrotyrosine methyl ester. The membrane-bound reporter group had different spectral properties, and a pK 3 units higher than in solution. In purple membranes, an isosbestic point between the 428nm absorption peak of nitrotyrosine methyl ester, and the bacteriorhodopsin 570nm chromophore seen in alkaline titration, indicated interactions between the reporter group and retinal. Modification of white membranes (bacterioopsin from R1mW strain) revealed similar, unusual spectral and ionization properties. Thus, the hydrophobic environment, not retinal interactions per se, are responsible for the ionization behavior of the reporter group. These results indicate that a carboxyl group is near the retinal chromophore of bacteriorhodopsin.

Bacteriorhodopsins↗
PubMed1983

Genetic and biochemical resolution of the chromophoric polypeptide of halorhodopsin.

Retinal-binding proteins in bacteriorhodopsin-deficient membranes of Halobacterium halobium have been separated on polyacrylamide gels after labeling with (3H)retinal. Four labeled polypeptides are observed: one at an Mr of 19,000, two distinct bands near 25,000, and one at 94,000. Comparing halorhodopsin-containing and halorhodopsin-deficient mutants and using ion translocation measurements and flash spectroscopy to test for the photoactive retinal pigments, we show that the lower of the two radiolabeled bands at 25,000 is the retinal-binding polypeptide of halorhodopsin. The identities of the other three polypeptides are not known, but one of them, probably the upper of the two 25,000 bands, is likely to be s-rhodopsin.

Bacteriorhodopsins↗
PubMed1984

Target size analysis of rhodopsin in retinal rod disk membranes.

Radiation inactivation of rhodopsin in situ using high-energy electrons gave a value for Mr of 20,200 by spectral assay, but 47,100 by assay of rhodopsin regeneration from opsin and 11-cis-retinal (sequence Mr = 38,840). No light/dark differences were seen. We conclude: (a) radiation inactivation measures the size of the functional unit, and the single hit hypothesis does not hold in our experiments; (b) 500 nm absorbance requires only about half the rhodopsin molecule to be intact, but reconstitution of rhodopsin from opsin requires the whole molecule; (c) we find no evidence for functional interactions between rhodopsin monomers in darkness or light.

Animals↗
PubMed1984

Diacylglycerol, 1-oleoyl-2-acetyl-glycerol, stimulates superoxide-generation from human neutrophils.

1-Oleoyl-2-acetyl-glycerol which activates Ca2+-activated phospholipid-dependent protein kinase, induced the superoxide-production of human neutrophils, while other diacylglycerols did not. The induction was independent of extracellular calcium and did not accompany the increase of the intracellular free calcium. The superoxide-release by the diacylglycerol was inhibited by retinal, the inhibitor of the protein kinase. The diacylglycerol stimulated the phosphorylation of at least 4 proteins in intact neutrophils, the phosphorylation of which was stimulated by phorbol 12-myristate 13-acetate, the activator of the protein kinase. These observations indicate the possible involvement of the kinase in the induction process.

Diglycerides↗
PubMed1984

Vitamin A acid-induced activation of Ca2+-activated, phospholipid-dependent protein kinase from rabbit retina.

Ca2+-activated, phospholipid-dependent protein kinase from rabbit retina was partially purified. Vitamin A acid (retinoic acid) stimulated this protein kinase in the presence of Ca2+, while other metabolites of vitamin A such as retinol or retinal were less effective. The order of the extent of phosphorylation of the various substrate proteins by this protein kinase was identical in the presence of vitamin A acid or phosphatidylserine. The major spots of the 32P labeled peptide from histone H1 phosphorylated in the presence of vitamin A acid by this protein kinase did not differ from those obtained from histone H1 phosphorylated in the presence of phosphatidylserine. Retinol caused a further enhancement of the enzymatic activity, whereas the addition of retinal inhibited the activation by vitamin A acid. Thus, vitamin A and its metabolites may play an important role in the regulation of Ca2+-activated, phospholipid-dependent protein kinase activity in the retina.

Animals↗
PubMed1986

Coordinate actions of arachidonic acid and protein kinase C in gonadotropin-releasing hormone-stimulated secretion of luteinizing hormone.

The relative contributions of arachidonic acid and protein kinase C during GnRH-stimulated LH release were investigated in cultured rat anterior pituitary cells. Maximal or near-maximal concentrations of arachidonic acid or the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate, were less effective than a maximal dose of GnRH in stimulating LH release. However, the effect of a combination of arachidonic acid and phorbol ester was equivalent with that of GnRH. The protein kinase C inhibitor, retinal, significantly reduced GnRH- and phorbol-induced, but not arachidonic acid-stimulated, LH release. The lipoxygenase inhibitors, 5,8,11,14-eicosatetraynoic acid and nordihydroguaiaretic acid, partially inhibited GnRH- and arachidonic acid-stimulated, but not phorbol-induced, LH secretion. Simultaneous addition of retinal and either lipoxygenase inhibitor completely abolished LH responses elicited by GnRH, as well as by combined treatment with arachidonic acid and the phorbol ester. These results suggest that hormone release is mediated by phospholipid-dependent mechanisms that are coordinated during the stimulation of LH secretion by GnRH.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1987

13-cis-retinal stimulates proliferation and induces intranuclear protein accumulation in the human mammary tumor cells MCF-7.

The human mammary tumor cells MCF-7 show enhanced proliferation when treated with low doses (10(-8)-10(-7) M) of 13-cis Retinal (a vitamin A derivative). These results are independent of the growth medium used. We describe a novel effect of 13-cis Retinal: the increased synthesis and accumulation of nuclear proteins in chronically treated cells. The cytoplasmic proteins and proteins released to the culture medium are transiently and oppositly modified. Moreover, chronic treated cells have growth advantages over the untreated counterparts in a clonogenic soft agar assay.

Breast Neoplasms↗
PubMed1989

Indirect evidence that protein kinase C plays a critical role in signal transduction of both vasopressin and corticotropin-releasing factor on pituitary cells in culture.

The possible role of protein kinase C (PKC) in the cyclic AMP-dependent mechanism of action of corticotropin-releasing factor (CRF) on proopiomelanocortin cells of anterior and intermediate pituitary glands was examined after pretreatment of cells in culture with the PKC inhibitor retinal or the phorbol ester PMA, which depletes cell stores of the kinase. We found that these drugs not only abolished ACTH response to PMA and vasopressin, which both activate PKC, but unexpectably also dampened by 80-90% the stimulatory effect of CRF. Cell treatment with retinal failed to prevent CRF-induced accumulation of cyclic AMP. Retinal and PMA pretreatments of intermediate pituitary cells likewise inhibited alpha-MSH secretion stimulated by CRF. These data provide evidence to suggest that the mechanism of action of CRF on pituitary cells involves both cyclic AMP and PKC messenger systems.

Animals↗
PubMed1989

The molecular basis of retinoic acid induced night blindness.

Drugs which affect the processing of vitamin A in the retina or pigment epithelium can cause ocular toxicity. It is shown here that the retinoic acids, which are used in the treatment of skin disorders and which cause night blindness, inhibit the ocular retinol dehydrogenases in an in vitro system. This is shown to lead to a decrease in the formation of the visual chromophore 11-cis-retinal, thus explaining why night blindness might occur.

Alcohol Oxidoreductases↗
PubMed1991

Photoisomerization of retinal at 13-ene is important for phototaxis of Chlamydomonas reinhardtii: simultaneous measurements of phototactic and photophobic responses.

A real-time automated method was developed for simultaneous measurements of phototactic orientation (phototaxis) and step-up photophobic response of flagellated microorganisms. Addition of all-trans retinal restored both photoresponses in a carotenoid-deficient mutant strain of Chlamydomonas reinhardtii in a dose-dependent manner. The phototactic orientation was biphasic with respect to both the light intensity and the concentration of retinal. All-trans retinal was more effective than 11-cis retinal to regenerate both photobehavioral responses. Analogs having locked 11-cis configurations and a phenyl ring in the side chain also induced photoresponses, although at concentrations more than two orders of magnitude higher than all-trans retinal. According to the present assay method, the responses were hardly detectable in cells incubated with retinal analogs in which the 13-ene was locked in either its trans or cis configuration. The results strongly suggest that the isomerization of the 13-14 double bond is important for photobehavioral signal transduction and that a single retinal-dependent photoreceptor controls both phototactic and photophobic responses.

Cell Movement↗
PubMed1989

Increased hepatic retinal dehydrogenase activity after phenobarbital and ethanol administration.

Cytosolic retinal dehydrogenase (EC 1.2.1.36, retinal: NAD+ oxidoreductase) activity was measured by assessing the conversion of retinal to retinoic acid by HPLC. In vitro, acetaldehyde, chloral hydrate and disulfiram were found to be inhibitors, whereas 95% of the activity remained in the presence of cyanide or in the absence of oxygen. In rats, retinal dehydrogenase activity prevailed over that of retinal oxidase. By contrast, in deermice, 80% of retinal oxidation was due to the oxidase rather than the retinal dehydrogenase activity in a normal strain (ADH+) as well as in one lacking alcohol dehydrogenase (ADH-). In ADH- deermice, retinal oxidase activity was greater than in ADH+ animals. In vivo, in the rat, chronic ethanol administration resulted in a significant increase of the dehydrogenase activity in the liver, but not in other tissues. After phenobarbital administration, hepatic retinal dehydrogenase activity was increased 8-fold, but no extrahepatic induction was observed. Conversely, feeding rats with a diet devoid of the precursor for the substrate (retinal) by replacing retinyl acetate with an equivalent amount of retinoic acid resulted in decreased retinal dehydrogenase activity. Under conditions in which retinal dehydrogenase activity is rate-limiting for the metabolism of retinal to retinoic acid, its induction after phenobarbital or ethanol administration may contribute to hepatic vitamin A depletion.

Aldehyde Oxidoreductases↗