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Thapsigargin protects human erythrocyte Ca(2+)-ATPase from proteolysis
1School of Biological Sciences, University of East Anglia, Norwich, UK.
Cell Calcium
|January 1, 1995
Summary
Thapsigargin slows the activation of the plasma membrane calcium ATPase (Ca2+-ATPase) by trypsin. This suggests thapsigargin may interfere with Ca2+-ATPase regulation in living cells.
Area of Science:
- Biochemistry
- Cell Biology
- Enzymology
Background:
- The plasma membrane calcium ATPase (Ca2+-ATPase) is crucial for maintaining calcium homeostasis.
- Thapsigargin is a known inhibitor of the endoplasmic reticulum Ca2+-ATPase, but its effects on plasma membrane Ca2+-ATPase are less understood.
Purpose of the Study:
- To investigate the effect of thapsigargin on the activation of plasma membrane Ca2+-ATPase by partial proteolysis.
- To determine if thapsigargin influences the enzyme's response to trypsin and calmodulin.
Main Methods:
- Studied intact human erythrocyte membranes and purified Ca2+-ATPase.
- Used trypsin for partial proteolysis and SDS-PAGE to analyze protein fragments.
- Assessed enzyme activation in the presence and absence of thapsigargin and calmodulin.
Main Results:
- Thapsigargin significantly slowed the rate of trypsin-induced activation of Ca2+-ATPase.
- Thapsigargin did not alter the pattern of proteolysis but delayed the appearance of tryptic fragments.
- Thapsigargin enhanced calmodulin-mediated activation of the enzyme.
Conclusions:
- Thapsigargin affects the kinetics of Ca2+-ATPase activation by proteolysis.
- While not directly inhibiting catalytic activity in vitro, thapsigargin may disrupt Ca2+-ATPase regulation in vivo.