Biomedical subjects

U Janssen-Timmen

Publications and source records attributed to U Janssen-Timmen.

22 records · Page 2Linked to original sources

PubMed1984

Cytoplasmic and cell surface structure of purified liver gap junctions revealed by freeze-drying.

After freeze-drying of purified liver gap junction plaques and vesicles the structural features of the inner and outer aspects of purified gap junctions were investigated. No structural details were seen on the cytoplasmic side of the connexions whereas on the cell surface side the connexions were organized in a paracrystalline pattern and exhibited a central depression or pore. We conclude that the central pore through each connexion varies in diameter along its length and that the closing site is located near the cytoplasmic face.

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PubMed1983

Immunocytochemical localization of the gap junction 26 K protein in mouse liver plasma membranes.

Specific binding sites for anti-26 K antibodies directed against the liver gap junction protein (26 K) were localized by immunoelectron microscopy in gap junction plaques purified from hepatic plasma membranes. Using immunofluorescence microscopy we found discrete fluorescent spots on plasma membranes in cross sections of liver tissues after incubation with anti-26 K antibodies. This is consistent with the notion of specific binding to gap junction plaques. Quantitative binding of anti-26 K antibodies was indirectly measured by the protein A-gold technique. We found that urea/detergent-treated, purified gap junction plaques bind 30-fold more anti-26 K antibodies than preimmune serum. Anti-26 K antibodies also bind specifically to native gap junction plaques within hepatic plasma membranes although only about one fifth as efficiently as to purified plaques. Possibly the anti-26 K antibodies raised after injection of SDS-denatured 26 K protein into rabbits recognize the cytoplasmic face of urea/detergent-treated plaques better than that of native plaques. Some, if not most, of the vesicular structures in preparations of purified plaques appear to be derived from split gap junction plaques and are probably sheets of gap junction hemichannels. In some vesicles the former cytoplasmic face of the hemichannels is turned outside, other vesicles have the former cell surface turned outside. The anti-26 K antibodies do not recognize any 26 K protein on the sheets of partially split gap junction plaques, on the heterogeneous vesicular structures, or on non-junctional areas of hepatic plasma membranes. These results suggest that the conformation of the 26 K protein in plaques must be different from that of the 26 K protein in earlier biosynthetic steps of plaque assembly.

Animals↗

PubMed1982

Immunological properties of gap junction protein from mouse liver.

Hepatic gap junctions were purified as plaques from BALB/c mice and separated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). Antisera were raised in rabbits and rats against gap junction plaques as well as protein bands of the following apparent molecular weights: 44K to 49K ("dimer" proteins), 26K, and 21K. Using an enzyme immunoassay, we found that the reactivities of the different antisera towards gap junction plaques decreased in the following order: anti-plaque antisera, anti-26K antisera, anti-"dimer" protein antisera, and anti-21K antisera. The gap junction protein bands separated by SDS-polyacrylamide gel electrophoresis were transferred by blotting onto nitrocellulose paper and the immunological cross-reactivities were compared: the anti-26K antisera reated with the dimer protein bands and the 26K band but did not cross-react with the 21K protein band. The rabbit anti-21K antiserum reacted weakly with the 21K protein. The missing immunological cross-reaction of the 26K and the 21K protein band can be most easily explained if both proteins were independent of each other. No inhibition of metabolic cooperation between fibroblastoid mouse 3T6 cells was observed in the presence of Fab fragments prepared from rabbit antiplaque antiserum or from rabbit anti 26K antiserum. When the total proteins of plasma membranes from mouse liver were separated by SDS-polyacrylamide electrophoresis, only the 26K protein reacted with rabbit anti 26K antiserum. This result opens the possibility for direct quantitation of gap junction protein in tissues and cell fractions.

Animals↗

PubMed1982

Biochemical and genetic investigations on gap junctions from mammalian cells.

Gap junction protein (26K) in mouse or rat liver has been studied using a rabbit antiserum directed against the sodium dodecylsulfate denatured 26K protein from mouse liver. The liver 26K protein has been localized in gap junction plaques of hepatic plasma membranes by immuno electron microscopy. Affinity purified anti-26K antiserum showed weak cross reactivity with mouse or bovine lens gap junction protein (MIP26). This result suggests some structural homology between the different gap junction proteins in liver and lens. After partial hepatectomy of young rats the liver 26K protein appears to be degraded and later resynthesized. A variant of established Chinese hamster fibroblastoid cells has been isolated and shown to be defective in metabolic cooperation via gap junctions.

Animals↗