Ca2+-Binding Proteins Located on the Cytoplasmic Face of the Lymphocyte Plasma Membrane
Three polypeptides of mol. wts.~68,000, 33,000 and 28,000 have been identified in Ca2+ -chelator extracts of purified preparations of lymphocyte plasma membrane (p.m.). They are preferentially associated with the actin-rich, Nonidet P40-insoluble fraction of the membrane and are not labelled by lactoperoxidase-catalyzed iodination of whole lymphocytes, suggesting that they are located on the cytoplasmic face of the p.m. The 68,000 mol. wt. protein, the most abundant of the three in the EGTA extract, has been purified from pig and human lymphocyte p.m. and partially characterized. It is a monomeric acidic protein with a single high-affinity Ca2+-binding site (KD = 1.2 μM). From their solubility with Ca2+ -chelators present, the 33,000 and 28,000 components seem to be Ca2+-binding proteins too.
KeywordsPolypeptide Composition Cytoplasmic Face Human Tonsil Imperial Cancer Research Fund Burkitt Lymphoma Cell Line
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