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Lactate dehydrogenase isoenzymes are present in matrix vesicles
R Hosokawa1, Y Uchida, S Fujiwara
1Department of Prosthetic Dentistry, Kyushu Dental College, Kitakyushu, Japan.
The Journal of Biological Chemistry
|July 25, 1988
Summary
Matrix vesicles contain lactate dehydrogenase (LDH), an enzyme found in chondrocyte cytosol. This suggests a specific uptake mechanism and potential for enzymatic quantification of matrix vesicles in calcification.
Area of Science:
- Biochemistry
- Cell Biology
- Skeletal Biology
Background:
- Matrix vesicles are key initiators of endochondral ossification.
- Understanding the molecular composition of matrix vesicles is crucial for studying bone formation.
- Lactate dehydrogenase (LDH) is a cytosolic enzyme in chondrocytes.
Purpose of the Study:
- To investigate the presence and localization of lactate dehydrogenase (LDH) within matrix vesicles.
- To explore the implications of LDH localization for matrix vesicle function and quantification.
Main Methods:
- Isolation of matrix vesicles from rabbit epiphyseal growth plates.
- Enzyme activity assays for lactate dehydrogenase and alkaline phosphatase.
- Differential enzyme activity measurements in the presence and absence of detergents.
Main Results:
- Lactate dehydrogenase activity was detected in isolated matrix vesicles, but only when detergents permeabilized the vesicle membrane, indicating intracellular localization.
- Alkaline phosphatase, an outer-surface marker, showed activity regardless of detergent presence.
- Lactate dehydrogenase was exclusively found in chondrocyte cytosol, not other subcellular fractions.
- Isolated matrix vesicles contained all five LDH isoenzymes but lacked other cytosolic enzymes.
Conclusions:
- Lactate dehydrogenase is specifically localized within matrix vesicles.
- A mechanism for selective uptake of cytosolic LDH into matrix vesicles likely exists.
- The presence of LDH offers a potential method for enzymatic quantification of matrix vesicles at calcification sites.