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Biomedical subjects

R S Liu

Publications and source records attributed to R S Liu.

At least 163 records · Page 9Linked to original sources
PubMed1986

Photosensitivity of 10-substituted visual pigment analogues: detection of a specific secondary opsin-retinal interaction.

The photosensitivities of the bovine rhodopsin and gecko pigment 521 analogues regenerated from C-10-substituted analogues of 11-cis- and 9-cis-retinals were determined by two different methods. A similar reactivity trend was noted for both pigment systems as revealed in the photosensitivity of the gecko pigments and relative quantum yields of the bovine analogues. The 10-fluoro-11-cis photopigments had a photosensitivity less than, but approaching, that of the native (11-cis) visual pigment while the 10-fluoro-9-cis photopigments had a much lower photosensitivity than the parent 9-cis regenerated pigment. The results are interpreted in terms of recently described models of rhodopsin architecture and of the primary molecular reaction of visual pigments to light. The unusually low photoreactivity of the 10-fluoro-9-cis pigment molecule is viewed as the result of a regiospecific hydrogen-bonding interaction of the electronegative fluorine atom to the opsin.

Animals↗
PubMed1986

Brain SPECT imaging with 99Tcm-hexamethylpropyleneamine oxime in the early detection of cerebral infarction: comparison with transmission computed tomography.

A new cerebral blood flow agent, 99Tcm-hexamethylpropyleneamine oxime (HM-PAO), was evaluated for early detection of acute cerebral infarction in conjunction with the transmission computed tomographic (CT) studies. The data from 22 cases were analysed. Results reveal that 99Tcm-HM-PAO enables the early detection of acute cerebral infarction prior to CT with rather proper depiction of the extent of physiological abnormality in the majority of patients. This promising result together with the lack of logistical problems will make 99Tcm-HM-PAO a useful and practical agent worldwide for diagnosing and managing acute cerebral infarction.

Brain↗
PubMed1985

The primary process of vision and the structure of bathorhodopsin: a mechanism for photoisomerization of polyenes.

A model for the primary process of vision is proposed, which involves a novel concerted-twist motion. Application of such motions to rhodopsin and bathorhodopsin successfully accounts for the properties of bathorhodopsin and related intermediates, including specific assignment of molecular structures to bathorhodopsin, to lumirhodopsin, and, less specifically, to hypsorhodopsin.

Isomerism↗
PubMed1985

Sequential uptake patterns of technetium-99m pyrophosphate in hepatoma.

Sequential liver scintiphotography with Tc-99m pyrophosphate (PYP) was used to prospectively evaluate its uptake patterns in hepatoma. The scintiphotos and time-activity curves of 40 cases were analyzed. Two distinct patterns of tumor activity were noted: gradual but complete extraction and trapping of Tc-99m PYP in hepatoma in 38% of the patients (group 1), and absence of subsequent Tc-99m PYP uptake in hepatoma after initial blood pool activity in 62% of the patients (group 2). Since extraction and trapping of Tc-99m PYP occur approximately in two fifths of the patients with hepatoma, we conclude that Tc-99m PYP liver scintigraphy is not worthwhile supplementing the conventional radionuclide studies for diagnosing hepatoma, even in the selected patients in the countries where the prevalence of hepatoma is high.

Carcinoma, Hepatocellular↗
PubMed1985

Technetium-99m HIDA hepatic lobar distribution and retention ratios in detection of intrahepatic lithiasis.

Technetium-99m HIDA hepatic lobar distribution and retention ratios were developed to evaluate patients with intrahepatic lithiasis. The data of 57 cases were analyzed. Results reveal a highly significant difference in these ratios between the patients and normal individuals. They are simple, objective, and easily obtainable. Thus, the determination of these ratios may replace [99mTc]HIDA sequential scintiphotography, which is qualitative and time consuming, for screening intrahepatic lithiasis.

Calculi↗
PubMed1984

Interaction of aromatic retinal analogues with apopurple membranes of Halobacterium halobium.

Absorption spectral properties of aromatic analogues of retinal with apopurple membrane of Halobacterium halobium were studied. The spectra of the all-trans forms were composed of two or more absorption bands. During incubation at 20 degrees C, an absorption band above 500 nm increased in intensity gradually at the expense of an absorption band in the shorter wavelength region with no isomerization of the chromophore. The longer wavelength species was shown to be the protonated form of the shorter wavelength species by changing the pH of the medium. Upon irradiation with blue light, the bandwidth of the spectrum became smaller with isomerization of the chromophore to its 13-cis form. Irreversible binding of protons on the membrane occurred during this process. The rate of the increase in the longer wavelength absorption band was especially low in the reaction with the all-trans form of retinal analogues having a bulky substituent at the para or meta positions of the phenyl ring. In contrast, the 13-cis isomer of aromatic retinal analogues gave a single absorption peak. The extent of the spectral shift upon binding to apopurple membranes was compared over a series of aromatic retinals, and the results were explained in terms of steric interactions of the chromophore with the protein.

Bacteriorhodopsins↗
PubMed1984

Independent sensitivity of human tumor cell lines to interferon and double-stranded RNA.

The antiproliferative effect of human interferons (IFNs) and double-stranded RNAs (dsRNAs) was measured in eight human tumor cell lines, five of which were derived from carcinomas of the bladder. Dose-response curves were generated for a 72-hr treatment period. The concentration of interferon or dsRNA necessary to inhibit tumor cell growth 50% compared to untreated cells was generated by linear regression analysis of the dose-response data. In the seven of eight cell lines in which a direct comparison could be made, IFN-beta was a more potent inhibitor than IFN-alpha. Polyriboinosinic acid X polyribocytidylic acid consistently gave an increased antiproliferative response compared to its mismatched analogue, rln X r(C12,U)n. Correlations could not be made between either IFN-alpha or IFN-beta and the dsRNA effect. No correlation was seen between IFN or dsRNA sensitivity and cell type, ability to bind IFN, growth rate, or tumorigenicity in nude mice. The antiproliferative effect of dsRNA was studied in the presence of antibodies against IFN-beta in HT1080 Cl 4, a cell line sensitive to both IFN and dsRNA, and A2182, a cell line relatively resistant to IFN-beta but sensitive to dsRNA. In both cell lines, the anti-IFN-beta antibodies inhibited the antiproliferative effect of the dsRNAs. After treatment with a concentration of dsRNA necessary to inhibit tumor cell growth 50% compared to untreated cells, a concentration of IFN-beta necessary to inhibit tumor cell growth 50% was induced in the HT1080 Cl 4 cells; however, only a low level of IFN-beta was detected in the culture medium of the A2182 cells.

Cell Division↗
PubMed1980

Aromatic retinal analogues and their interaction with cattle opsin.

The preparation of seven aromatic analogues of retinal, the isolation and characterization of their geometric isomers, and the interaction of these isomers with cattle opsin are reported. Within certain limitations, it has been demonstrated that stable aromatic rhodopsin analogues can be prepared. In general, the stereoselectivity of isomers of these compounds in their interaction with opsin and the absorption properties of the resultant pigments are similar to those of the parent retinal.

Animals↗
PubMed1980

Photochemical studies of 7-cis-rhodopsin at low temperatures. Nature and properties of the bathointermediate.

The photoreaction of 7-cis-rhodopsin derived from 7-cis-retinal and cattle opsin was studied by low-temperature spectrophotometry. Upon irradiation of 7-cis-rhodopsin at liquid nitrogen temperature (-190 degrees C) with blue light, its spectrum shifted to the longer wavelengths, indicating the formation of a bathoproduct. The bathoproduct thus formed was found to be identical with bathorhodopsin formed from rhodopsin in their spectroscopic, photochemical, and thermal properties. Therefore, we believe that the bathoproduct is, in fact, bathorhodopsin. The fact that 7-cis-rhodopsin can be readily converted to rhodopsin and to 9-cis-rhodopsin shows that the identical retinal binding site of opsin is involved in the three isomeric rhodopsins. These results appear to be consistent with the notion that the chromophore of bathorhodopsin is a twisted all-trans isomer, which is readily obtainable from the 7-cis, 9-cis, and 11-cis isomers.

Animals↗