title: Calmodulin-binding proteins that interact with actin filaments in a Ca2+-dependent flip-flop manner: survey in brain and secretory tissues.
abstract: Regulatory actions of calmodulin on the contractile apparatus and cytoskeleton of smooth muscle and nonmuscle tissue are mediated by a number of specific calmodulin-binding proteins that bind to F-actin in a flip-flop manner--i.e., they bind to calmodulin or F-actin depending on the presence or absence, respectively, of Ca2+. A survey for such proteins in brain, adrenal gland, and pituitary gland identified six polypeptides on polyacrylamide gels--Mr 340,000 (band 1), Mr 240,000/235,000 doublet (band 2), Mr 150,000 (band 3), Mr 129,000 (band 4), Mr 105,000 (band 5), and Mr 94,000 (band 6)--as flip-flop-regulated calmodulin- and F-actin-binding polypeptides. In addition to these polypeptides, a Mr 58,000 non-flip-flop calmodulin-binding actin-binding polypeptide (band 7) was found in all tissues examined. Band 2 was identified as calspectin (spectrin-related protein; fodrin). The flip-flop regulation of calspectin required the presence of a heat-labile nondialyzable factor contained in a supernatant fraction of brain homogenates. Band 1 was distinct from microtubule-associated proteins (MAPs) 1 and 2. However, when band 1 polypeptide was kept on ice 3 days, it converted to a lower molecular weight doublet that migrated with MAP2 on NaDodSO4 gel electrophoresis. Bands 1 and 2 were found in all tissues examined.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000302:Adrenal Cortex / Q000378:metabolism; D000313:Adrenal Medulla / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins; D002417:Cattle; D007700:Kinetics; D008970:Molecular Weight; D009928:Organ Specificity; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D010904:Pituitary Gland, Posterior / Q000378:metabolism
chemical_list: D000199:Actins; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D010749:Phosphoprotein Phosphatases; D002118:Calcium