Molecular Characterization of Plasma Membrane Calcium Pump Isoforms
The ability to precisely control the free intracellular Ca2+ concentration is of utmost importance for eukaryotic cell function. Membrane-intrinsic transport systems play an essential role in this intracellular Ca2+ regulation (1). Among the Ca2+ transport system of the plasma membrane, ATP-driven Ca2+ pumps have attracted increasing attention over the past few years. Because of their very low abundance (≤0.1% of the total membrane protein) these enzymes have traditionally been difficult to study on a biochemical level. In this situation, however, human red blood cells have proved to be an invaluable source for the analysis and the purification of these molecules. This is mainly due to the absence in mature human erythrocytes of an extensive intracellular membrane network as well as to the easy availability of large quantities of these cells. The rapid accumulation of molecular details concerning the regulation, structure and function of plasma membrane Ca2+ pumps has thus been largely due to the development of an efficient purification procedure for this enzyme from human erythrocytes (2), and to the recent success in the application of refined methods of protein biochemistry and recombinant DNA technology (3). In this report we shall begin with a brief summary of the general characteristics of typical plasma membrane Ca2+ pumps and will then describe the recent advances made in the molecular characterization of these enzymes. Particular attention will be paid to the molecular genetic basis of isoform diversity and to comparative aspects of their structural, functional and regulatory properties.
KeywordsHuman Erythrocyte Calcium Pump cAMP Dependent Phosphorylation Complete Primary Structure Total Membrane Protein
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