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Biomedical subjects

R Crouch

Publications and source records attributed to R Crouch.

At least 55 records · Page 3Linked to original sources
PubMed1984

Canine retinal superoxide dismutase: identity with the erythrocyte enzyme.

Superoxide dismutase has been isolated from canine retina and compared to the commercial erythrocyte enzyme. The two enzymes have been characterized by biochemical and immunochemical methods. By the criteria used (enzymatic activity, immunoactivity, absorption spectra, electrophoretic properties, amino acid analyses and peptide maps), the two enzymes are completely homogeneous.

Amino Acids↗
PubMed1984

Cycloheptatrienylidene analog of 11-cis retinal. Formation of pigment in photoreceptor membranes.

In biochemical and electrophysiologic studies employing the bullfrog (Rana catesbeiana) and the rat, the authors examined the interaction of opsin and an 11-cis-locked analog of retinal. In previously bleached preparations of bullfrog receptor outer segments (ROS) and isolated retinas, incubation with the aldehyde form (I) of the analog leads to the appearance of a pigment that is degraded slowly by hydroxylamine but is relatively resistant to photolysis. In the ROS preparation, the analog pigment (lambda max of difference spectrum congruent to 497 nm) also forms on incubation with NADP+ and the alcohol form (II) of the analog. In vitamin A deprived rats possessing only approximately 45% of the normal complement of rhodopsin, intraperitoneal injection of II leads within 1 day to the appearance of the analog pigment in the photoreceptors, at levels representing a major fraction of the opsin initially available for pigment formation. Formation of the analog pigment appears to have no significant effect on the sensitivity of electroretinographic b-wave responses recorded from the rat eye; furthermore, administration of II appears to suppress the sensitizing activity of all-trans retinol injected 1 day later. The data are discussed in relation to other studies examining chromophore-opsin interactions and electrophysiologic changes associated with the formation of rhodopsin in situ.

Animals↗
PubMed1981

Possible association of angiosarcoma with oral contraceptive agents.

Angiosarcoma of the liver has been reported to be associated with the long-term use of androgenic-anabolic and oestrogenic steroids. It has been suggested that this tumour might develop in women after long-term exposure to oral contraceptive steroids, although this association has not yet been reported. We present here the clinical and pathological findings in a 42-year-old woman who died of hepatic angiosarcoma after taking oral contraceptive steroids for 10 years.

Adult↗
PubMed1981

Photochemical and functional properties of bacteriorhodopsins formed from 5,6-dihydro- and 5,6-dihydrodesmethylretinals.

5,6-Dihydroretinal and 5,6-dihydro-1,1,5,9,13-desmethylretinal are synthesized, and their all-trans isomers are shown to form pigment analogues (lambda max at 475 and 460 nm, respectively) of bacteriorhodopsin (purple membrane protein). The shift of the absorption maximum od the pigment from that of the protonated Schiff base of the chromophore for 5,6-dihydrobacteriorhodopsin is small compared to that of the native pigment, suggesting that negative charges similar to those controlling the lambda max of visual pigment rhodopsin exist near the cyclohexyl ring. Both pigment analogues undergo reversible light-induced spectral shifts reflecting cyclic photoreactions of the pigments. These results indicate that the absence of the C-5--C-6 double bond and of the five methyl groups of retinal does not abolish the photochemistry of these pigment analogues and strongly suggest that these structural features are not directly required for the photoreactions of native bacteriorhodopsin. The apparent rates of the photochemical transformations of these artificial pigments are quite different from those of bacteriorhodopsin. A working hypothesis is proposed for the photocycle of the pigment analogues, which includes a slower light-induced cycling rate (for the light-adapted pigments) than that of native bacteriorhodopsin and an increased rate of dark adaptation. When incorporated into egg lecithin vesicles both pigment analogues show proton pumping ability, again indicating that the missing double bond and the methyl groups are not structurally required for the function of the pigments.

Bacteriorhodopsins↗
PubMed1980

Bathoproducts of rhodopsin, isorhodopsin I, and isorhodopsin II.

Bathorhodopsins were prepared by partially (10--15%) photoconverting bovine rhodopsin (11-cis chromophore) or isorhodopsin I (9-cis chromophore) at 77 degrees K; care was taken to avoid establishing photostationary states. The absorption spectra calculated for the bathorhodopsins derived from the two parent pigments are identical in their lambda max 'S, bandwidths, and extinction coefficients. This result provides further support for the hypothesis that bathorhodopsin is a common intermediate between an 11-cis pigment (rhodopsin) and a 9-cis one (isorhodopsin I) and thus probably has an all-trans chromophore. This in turn is strong evidence for the cis-trans isomerization model of the primary event in vision. The spectrum of the bathoproduct of isorhodopsin II (9,13-dicis chromophore) is different from the other pigments' bathoproducts.

Animals↗
PubMed1978

Sensitizing activity of 9,13-dicis retinal in bleached photoreceptors of the skate.

9,13-dicis Retinal was externally applied to photoreceptors of isolated skate retina that previously had been desensitized by bleaching irradiation. This treatment led to a significant lowering of photoreceptor threshold and to the intracellular formation of isorhodopsin II, an artificial visual pigment containing 9,13-dicis retinal as its chromophore. These results suggest that isorhodopsin II can function in situ to promote an increase in the visual sensitivity of skate photoreceptors.

Animals↗
PubMed1976

Molecular flow resonance Raman effect from retinal and rhodopsin.

We have performed resonance enhanced Raman measurements of retinal isomers in solution (all-trans, 11-cis, 9-cis, and 13-cis) and cetyltrimethylammonium bromide (CTAB) detergent extracts of bovine rhodopsin near physiological temperatures (17 degrees C). In order to measure these photolabile systems, we have developed a general technique which allows Raman measurements of any photosensitive material. This technique involves imposing a molecular velocity transverse to the Raman exciting laser beam sufficient to ensure that any given molecule moves through the beam so that it has little probability of absorbing a photon. We have also measured the resonance Raman spectra of crystals of the same retinal isomers. The data show that each isomer has a distinct and characteristic Raman spectra and that the spectrum of 11-cis-retinal is quite similar but not identical with that of rhodopsin and similarly for 9-cis-retinal compared with isorhodopsin. In agreement with previous work, the Raman data demonstrate that retinal and opsin are joined by a protonated Schiff base. Due to the fact that the Raman spectra of 11-cis-retinal (solution) and rhodopsin show bands near 998 and 1018 cm(-1), a spectral region previously assigned to C-Me stretching motions, it is suggested that 11-cis-retinal in solution is compased of a mixture of 12-s-trans and 12-s-cis, and that the conformation of rhodopsin is (perhaps distorted) 12-s-trans.

Circular Dichroism↗
PubMed1976

Photosensitive pigments formed with rat opsin.

Photosensitive pigments are formed in vitro from rat opsin with the rods in suspension or as digitonin solutions. Rhodopsin, isorhodopsin I, and isorhodopsin II were generated with 11-cis, 9-cis and 9, 13-dicis retinal, respectively. An isorhodopsin I analogue was formed on combination with 9-cis 13-desmethyl-14-methylretinal. The absorption spectra and photosensitivities of these pigments were found to be similar to the corresponding bovine pigments although the rates of formation are several fold slower.

Animals↗
PubMed1975

Isorhodopsin II: artificial photosensitive pigment formed from 9,13-dicis retinal.

We have found that in addition to the 11-cis and 9-cis isomers of retinal which are known to couple with the visual pigment apoprotein opsin to form pigments, a third isomer 9,13-dicis retinal also will form a pigment. That this isomer is indeed bound to opsin has been shown unequivocally by removing the chromophore without isomerization and subsequent identification by high-speed liquid chromatography. Using similar techniques, we have shown that the product of bleaching by light of all three pigments in Trition X-100 is the all-trans isomer. This specificity in the product of bleaching, as with many other properties of visual pigments, is not shared by the free chromophore. Of particular interest is that when 9,13-dicis retinal is combined with opsin to form a pigment, a single photon can isomerize it about two double bonds, to the all-trans isomer.

Binding Sites↗
PubMed1972

Degradation of DNA RNA hybrids by ribonuclease H and DNA polymerases of cellular and viral origin.

Ribonuclease H from human KB cells, chick embryos, calf thymus, avian myeloblastosis virus, and Rous associated virus specifically degrades the RNA of DNA.RNA hybrids, producing mono- and oligoribonucleotides terminated in 5'-phosphates. The cellular RNase H is an endonuclease, whereas the viral enzyme appears to be an exonuclease. Viral DNA polymerase and RNase H copurify through all separation steps. Therefore, RNase H activity is an intrinsic part of the viral DNA polymerase. DNA.RNA hybrids are also degraded by nucleases associated with cellular DNA polymerases and by exonuclease III. However, these nucleases differ from RNase H in their ability to degrade both strands of DNA.RNA hybrids.

Animals↗