(Journal Article): Carbonic Anhydrase: In the Driver's Seat for Bicarbonate Transport
Sterling D, Reithmeier RAF, Casey JR (Membrane Transport Group and CIHR Group in Molecular Biology of Membrane Proteins, Department of Physiology, University of Alberta. Edmonton, Canada. CIHR Group in Membrane Biology, Department of Medicine, University of Toronto. Toronto, Canada,
joe.casey@ualberta.ca
)
IN:
JOP. J Pancreas (Online)
2001; 02(4 Suppl.):165-170
ABSTRACT: Carbonic anhydrases are a widely expressed family of enzymes that catalyze the reversible reaction: CO(2) + H(2)O = HCO(3)(-) + H(+). These enzymes therefore both produce HCO(3)(-) for transport across membranes and consume HCO(3)(-) that has been transported across membranes. Thus these enzymes could be expected to have a key role in driving the transport of HCO(3)(-) across cells and epithelial layers. Plasma membrane anion exchange proteins (AE) transport chloride and bicarbonate across most mammalian membranes in a one-for-one exchange reaction and act as a model for our understanding of HCO(3)(-) transport processes. Recently it was shown that AE1, found in erythrocytes and kidney, binds carbonic anhydrase II (CAII) via the cytosolic C-terminal tail of AE1. To examine the physiological consequences of the interaction between CAII and AE1, we characterized Cl(-)/HCO(3)(-) exchange activity in transfected HEK293 cells. Treatment of AE1-transfected cells with acetazolamide, a CAII inhibitor, almost fully inhibited anion exchange activity, indicating that endogenous CAII activity is essential for transport. Further experiments to examine the role of the AE1/CAII interaction will include measurements of the transport activity of AE1 following mutation of the CAII binding site. In a second approach a functionally inactive CA mutant, V143Y, will be co-expressed with AE1 in HEK293 cells. Since over expression of V143Y CAII would displace endogenous wild-type CAII from AE1, a loss of transport activity would be observed if binding to the AE1 C-terminus is required for transport.
TYPE OF PUBLICATION: Round Table
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