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Identification of ribophorins in rough microsomal membranes from different organs of several species
Abstract:
Microsomes prepared from several animal sources were analyzed for the presence of proteins corresponding to the ribophorins (I and II) which have been previously characterized in rat liver rough microsomes and appear to be involved in the binding of polysomes to endoplasmic reticulum membranes. In rough microsomal membranes from rat lacrimal gland, rabbit liver, dog and chicken pancreas, and mouse myeloma, ribophorin-like polypeptides with similar electrophoretic mobilities were detected by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. In all cases the polypeptides remained associated with sedimentable polysomes after solubilization of the microsomal membranes with nonionic detergents. Ribophorin-like polypeptides were absent from smooth microsomes. Antibodies raised against each rat liver ribophorin, purified by preparative sodium dodecyl sulfate/polyacrylamide gel electrophoresis, immunoprecipitated only the corresponding polypeptide, indicating no crossreactivity between ribophorins I and II. These antibodies also immunoprecipitated the homologous ribophorins found in microsomal preparations from other organs and species.
Insights
Ribophorins, proteins involved in polysome binding to endoplasmic reticulum membranes, were found in rough microsomes across various animal species. These ribophorin-like polypeptides are absent in smooth microsomes.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Ribophorins (I and II) are proteins previously identified in rat liver rough microsomes.
- These proteins are implicated in the binding of polysomes to endoplasmic reticulum (ER) membranes.
Purpose of the Study:
- To investigate the presence and characteristics of ribophorin-like proteins in rough microsomes from various animal sources.
- To determine if ribophorins are conserved across different species and tissues.
Main Methods:
- Sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) was used to analyze microsomal proteins.
- Antibodies against rat liver ribophorins were generated for immunoprecipitation studies.
- Microsomal membranes were solubilized with nonionic detergents to assess polypeptide association with polysomes.
Main Results:
- Ribophorin-like polypeptides with similar electrophoretic mobilities were detected in rough microsomes from rat lacrimal gland, rabbit liver, dog and chicken pancreas, and mouse myeloma.
- These polypeptides remained associated with sedimentable polysomes after detergent solubilization.
- Ribophorin-like polypeptides were absent in smooth microsomes.
- Antibodies showed no cross-reactivity between ribophorins I and II but recognized homologous proteins in other species.
Conclusions:
- Ribophorin-like proteins are conserved in rough ER membranes across diverse animal species.
- These proteins are specifically associated with rough microsomes and polysomes.
- Ribophorins I and II are distinct entities with species-specific homologous counterparts.