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Calcium pyrophosphate dihydrate (CPPD) crystal dissolution by alkaline phosphatase: interaction of alkaline
1Department of Pathology, Mount Sinai Hospital, Toronto, ON, Canada.
The Journal of Rheumatology
|January 1, 1995
Summary
Alkaline phosphatase (ALP) binds specifically to certain faces of calcium pyrophosphate dihydrate (CPPD) crystals, facilitating their dissolution. This nonenzymatic interaction is key to understanding CPPD crystal clearance.
Area of Science:
- Biochemistry
- Crystallography
- Rheumatology
Background:
- Alkaline phosphatase (ALP) is known to dissolve calcium pyrophosphate dihydrate (CPPD) crystals.
- Dissolution is more effective when ALP is in close proximity to CPPD crystals.
Purpose of the Study:
- To investigate the in vitro mechanism of ALP interaction with CPPD crystals.
- To elucidate the binding and dissolution process at a molecular level.
Main Methods:
- Incubation of ALP with CPPD crystals in an in vitro model.
- Utilized fluorescein isothiocyanate-conjugated ALP (FITC-ALP) for visualization.
- Employed alkaline phosphatase product staining and scanning electron microscopy.
Main Results:
- ALP demonstrated preferential binding to the small end faces (optical 010 faces) of CPPD crystals.
- Etch pits, indicating dissolution, were observed alongside ALP binding.
- ALP's pyrophosphohydrolytic activity was detected concurrently with crystal binding.
Conclusions:
- ALP exhibits stereoselective binding to CPPD crystals, primarily on the 010 faces.
- The binding mechanism is nonenzymatic, distinct from ALP's enzymatic activity, and influenced by ions.
- CPPD crystal dissolution rate appears limited by the surface area available on these specific crystal faces for ALP binding.