Characterization of Ca(2+)-ATPase in rod outer segment disk membranes
I Panfoli1, A Morelli, I M Pepe
1Istituto Policattedra di Chimica Biologica, Università di Genova, Italy.
Biochemical and Biophysical Research Communications
|October 28, 1994
Summary
This study characterizes the calcium pump in retinal disk membranes, revealing its unique properties distinct from plasma membrane calcium pumps. These findings suggest its role in regulating intracellular calcium levels within photoreceptor cells.
Area of Science:
- Biochemistry
- Cell Biology
- Neuroscience
Background:
- Rod outer segment disk membranes play a crucial role in vertebrate photoreceptor function.
- Understanding the mechanisms of intracellular calcium regulation is vital for comprehending visual signal transduction.
Purpose of the Study:
- To characterize the Ca(2+)-pump in rod outer segment disk membranes.
- To differentiate its properties from other calcium pumps, particularly plasma membrane Ca(2+)-ATPases.
Main Methods:
- Isolation and characterization of the Ca(2+)-pump from disk membranes.
- Inhibition studies using thapsigargin.
- Proteolytic digestion (calpain and trypsin) to analyze protein fragments.
- Comparison with Ca(2+)-ATPase from red blood cells as a control.
Main Results:
- The 100 kDa phosphoprotein exhibited an aspartylphosphate intermediate (E-P).
- Complete inhibition by thapsigargin and resistance to calpain digestion were observed.
- Tryptic digestion yielded two autophosphorylatable fragments (approx. 55 and 35 kDa).
- These characteristics align with sarcoplasmic/endoplasmic reticulum calcium pumps, not plasma membrane pumps.
Conclusions:
- The Ca(2+)-pump in disk membranes shares properties with intracellular calcium stores.
- Its distinct characteristics differentiate it from plasma membrane Ca(2+)-ATPases.
- The pump likely functions in intracellular calcium buffering within vertebrate photoreceptors.
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