title: Quantification and characterization of regulin, a Mr-230,000 highly elongated protein of rabbit reticulocytes.
abstract: Procedures are described by which regulin in rabbit reticulocytes was quantified and isolated in relatively large amounts. In these cells the protein occurs at a ratio of about 1.1-1.6 regulin monomers/spectrin tetramer, corresponding to 80,000-100,000 molecules of Mr-230,000 regulin/cell. Erythrocytes contain less than 12% of the amount of regulin in reticulocytes and the protein has not been detected in non-erythroid cells. Regulin was found primarily in the cytosolic fraction of lysed reticulocytes. It appears to be unusually sensitive to proteolysis by Ca2+-activated thiol proteases. Isolation of Mr-230,000 undegraded regulin was accomplished by the use of protease inhibitors including N-ethylmaleimide. A striking characteristic of regulin is its tendency to aggregate in neutral solution of low ionic strength. Physical studies of the isolated protein indicate that it has a highly elongated form in solution. The protein has no known enzymatic activity but was shown previously to interact with and increase the enzymatic activity of a protein phosphatase. The properties of regulin suggest that it may have a structural function but it appears to be physically and immunologically distinct from known proteins. It is suggested that regulin may contribute to a gel matrix within the cytoplasm of reticulocytes.
authors.affiliation: Clayton Foundation Biochemical Institute, Department of Chemistry, University of Texas, Austin 78284.
authors.forename: G
authors.initials: G
authors.lastname: Zardeneta
authors.forename: G
authors.initials: G
authors.lastname: Kramer
authors.forename: B
authors.initials: B
authors.lastname: Hardesty
mesh_terms: D000596:Amino Acids / Q000097:blood; D000818:Animals; D002449:Cell Aggregation; D002850:Chromatography, Gel; D003598:Cytoskeletal Proteins / Q000097:blood* / Q000302:isolation & purification; D003600:Cytosol / Q000032:analysis; D004591:Electrophoresis, Polyacrylamide Gel; D004912:Erythrocytes / Q000032:analysis; D011817:Rabbits; D012156:Reticulocytes / Q000032:analysis*; D013049:Spectrin / Q000097:blood; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship
chemical_list: D000596:Amino Acids; D003598:Cytoskeletal Proteins; D013049:Spectrin