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Novel components and enzymatic activities of the human erythrocyte plasma membrane calcium pump
R N Reusch1, R Huang, D Kosk-Kosicka
1Department of Microbiology, Michigan State University, East Lansing 48824, USA. rnreusch@msu.edu
Abstract:
The plasma membrane Ca2+ pump is essential for the maintenance of cystolic calcium ion concentration levels in eukaryotes. Here we show that the Ca2+-ATPase, purified from human erythrocytes, contains two homopolymers, poly(3-hydroxybutyrate) (PHB) and inorganic polyphosphate (polyP), which form voltage-activated calcium channels in the plasma membranes of Escherichia coli and other bacteria. Furthermore, we demonstrate that the plasma membrane Ca2+-ATPase may function as a polyphosphate kinase, i.e. it exhibits ATP-polyphosphate transferase and polyphosphate-ADP transferase activities. These findings suggest a novel supramolecular structure for the functional Ca2+-ATPase, and a new mechanism of uphill Ca2+ extrusion coupled to ATP hydrolysis.