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C A Converse

Publications and source records attributed to C A Converse.

30 records · Page 2Linked to original sources
PubMed1986

Short-term organ culture of the retinal pigment epithelium in microtitration plates: ultrastructural studies.

Microtitration plates were used to culture simultaneously multiple, small (6 mm diameter) explants of bovine retinal pigment epithelium (RPE). Evaluation of tissue by light microscopy and by scanning and transmission electron microscopy after various incubation periods up to 6 h showed that RPE maintained in this system retains near normal morphology. Initially, the explanted RPE lacks apical microvilli, but during the first 2-3 h in culture recovery of apical microvilli occurs. The results suggest that the system is suitable for short-term maintenance of RPE for experimental purposes. Moreover, the ability to culture up to 16 explants from one bovine eye aids statistical evaluation of RPE behaviour under varying experimental conditions.

Animals↗
PubMed1985

D-[3H]-galactose incorporation in the bovine retina: specific uptake and transport of the radiolabel in cones.

When bovine neural retinas are incubated in Krebs-Henseleit buffer with D-[3H]-galactose, autoradiography reveals that there is a rapid uptake of the tritium label into the inner segments of cones, but not of rods. Pulse--chase studies show that the label is first associated with the Golgi apparatus in the cones, then appears to travel around the nucleus and along the cone fibre (homologous to an axon) to the synaptic pedicle. The cone-specific label travels along the fibre at a rate of about 0.5-1.0 mm per day. Label is also found in endothelial cells and Müller cells, but does not persist in the Müller cells as long as in the cones. The striking difference between rod and cone labelling may reflect fundamental differences in the neurochemistry of these two photoreceptor cell types.

Animals↗
PubMed1983

Plasma lipid abnormalities in retinitis pigmentosa and related conditions.

Plasma samples obtained from 69 fasting retinitis pigmentosa (RP) patients and 110 controls were assayed for cholesterol, triglycerides, lipoproteins, and fatty acids. It was found that many RP patients were hyperlipidaemic compared to their spouses and siblings, as well as compared to unrelated controls. This hyperlipideaemia was particularly severe in men over 35 years of age, and in hemizygotes in X-linked families. In contrast, hypocholesterolaemia was observed in albipunctate retinal dystrophy. Plasma fatty acid titres were, in general, similar in RP patients and controls; however, patients in three families (two X-linked, one autosomal dominant) showed a significant reduction in docosahexaenoic acid (C22:6) compared to their unaffected relatives. These various plasma lipid abnormalities may reflect disorders in lipid metabolism which also may lead to retinal dystrophy.

Adult↗
PubMed1976

Energetics of primary processes in visula escitation: photocalorimetry of rhodopsin in rod outer segment membranes.

A sensitive technique for the direct calorimetric determination of the energetics of photochemical reactions under low levels of illumination, and its application to the study of primary processes in visula excitation, are described. Enthlpies are reported for various steps in the bleaching of rhodopsin in intact rod outer segment membranes, together with the heats of appropriate model reactions. Protonation changes are also determined calorimetrically by use of buffers with differing heats of proton ionization. Bleaching of rhodopsin is accompanied by significant uptake of heat energy, vastly in excess of the energy required for simple isomerization of the retinal chromophore. Metarhodopsin I formation involves the uptake of about 17 kcal/mol and no net change in proton ionization of the system. Formation of metarhodopsin II requires an additional energy of about 10 kcal/mol and involves the uptake on one hydrogen ion from solution. The energetics of the overall photolysis reaction, rhodopsin leads to opsin + all-trans-retinal, are pH dependent and involve the exposure of an additional titrating group on opsin. This group has a heat of proton ionization of about 12 kcal/mal, characteristic of a primary amine, but a pKa in the region of neutrality. We suggest that this group is the Schiff base lysine of the chromophore binding site of rhodopsin which becomes exposed on photolysis. The low pKa for this active lysine would result in a more stable retinal-opsin linkage, and might be induced by a nearby positively charged group on the protein (either arginine or a second lysine residue). This leads to a model involving intramolecular protonation of the Schiff base nitrogen in the retinal-opsin linkage of rhodopsin, which is consistent with the thermodynamic and spectroscopic properties of the system. We further propose that the metarhodopsin I leads to metarhodopsin II step in the bleaching sequence involves reversible hydrolysis of the Schiff base linkage in the chromophore binding site, and that subsequent steps are the result of migration of the chromophore from this site.

Animals↗
PubMed1975

Membrane protein analysis by two-dimensional immunoelectrophoresis.

Water-soluble membrane proteins may be analyzed by a new, rapid technique that combines electrophoresis on high-resolution sodium dodecyl sulfate (SDS) polyacrylamide gels and immunoelectrophoresis. After separation in the first dimension by electrophoresis in SDS, the proteins are subjected to a second electrophoresis at right angles through a two-layered buffered agarose gel. They first pass through a layer containing Lubrol PX which forms complexes with free SDS and then into an antiserum layer where antigen-antibody precipitates form. Precipitin arcs appear at positions corresponding to the antigens separated in the first dimension. The effectiveness of the technique was demonstrated with frog and cattle opsins, human erythrocyte membrane proteins, and their rabbit antiserums and for several water soluble proteins. By this method two fundamental parameters, molecular weight and antigenicity, may be readily used for analysis of membrane proteins.

Cell Membrane↗
PubMed1975

Membrane biosynthesis in the frog retina: opsin transport in the photoreceptor cell.

Rhodopsin biosynthesis and transport in the photoreceptor cell have been analyzed by subcellular fractionation of frog retinas after short periods of radioactive amino acid incorporation in vivo. Labelled membrane proteins were identified by autoradiography or sodium dodecyl sulfate-polyacrylamide gels. One of the most intensly labeled proteins in retina had a molecular weight comparable to opsin isolated from purified rod outer segments (ROS). Incorporation of label into this protein was rapid; the relative specific activity then diminished after the first 2 hr as radioactivity was transferred from retinal subcellular fractions to ROS. The kinetics of this transfer resembled rates previously observed by Hall et al. (Hall, M. O., Bok, D., and Bacharach, A.C.E. (1969), J. Mol. Biol. 45, 397). To identify the rapidly labeled protein as opsin we devised a new technique of two-dimensional immunoelectrophoresis of detergent solubilized membrane proteins. Antibodies were prepared against both whole ROS and opsin. After initial separation of retinal proteins on sodium dodecyl sulfate-polyacrylamide gels, a second dimension of electrophoresis in agarose, containing antisera, resulted in the formation of specific immunoprecipitates. Immunochemical analysis of all membranous and soluble retinal subcellular fractions indicated that newly synthesized opsin was membrane bound upon completion of synthesis. At no period of incorporation was a soluble form of newly synthesized opsin detectable. On this basis, we suggest that this protein is apparently transported as a water-insoluble membrane-bound molecule through the cytoplasm or along membranes of the inner segment to its assembly site near the base of the outer segment.

Amino Acids↗