Disposition of preformed mineral in matrix vesicles. Internal localization and association with alkaline phosphatase
Studies were made on the disposition of mineral ions in matrix vesicles (MV) and their relationship to alkaline phosphatase by treatment of MV-enriched microsomes (MVEM) with graded levels of Ca2+-chelating agents to complex accessible ions, fractionation of MVEM on hypertonic sucrose gradients at two different pH values (7.5 and 8.0) to evaluate for the presence of calcium phosphate mineral, and passage of MVEM through cation-exchange columns to determine the accessibility of the Ca2+. The effect of removal of Ca2+ and Pi on subsequent ability of MVEM to induce mineral formation from synthetic cartilage lymph was also determined. Passage through cation-exchange columns revealed that MV Ca2+ was not freely exchangeable, but coeluted in the void volume with alkaline phosphatase. However, upon incubation in synthetic cartilage lymph, progressively more Ca2+ was retained by the column. These findings indicate that, initially, the majority of Ca2+ in MVEM is internal and not readily exchangeable, but as Ca2+ accumulates, progressively more becomes external. The mineral in MV is labile and readily susceptible to loss; treatment with graded levels of EGTA removed major portions of the original Ca2+ and Pi. 45Ca uptake by these mineral-depleted MV was markedly reduced, even in the presence of alkaline phosphatase substrates. Sucrose gradient fractionation of MVEM caused extensive loss of Pi, but not Ca2+, from the low-density alkaline phosphatase-rich fractions. This reveals that Ca2+ and Pi are not initially coupled together: Pi is largely soluble, whereas Ca2+ must be tightly bound. In the high-density vesicles, large amounts of both Ca2+ and Pi are present.
- Research Organization:
- Univ. of South Carolina, Columbia
- OSTI ID:
- 6127771
- Journal Information:
- J. Biol. Chem.; (United States), Vol. 262:22
- Country of Publication:
- United States
- Language:
- English
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ALKALINE PHOSPHATASE
ENZYME ACTIVITY
MINERALS
BIOLOGICAL LOCALIZATION
CALCIUM 45
CALCIUM COMPOUNDS
CATIONS
CHELATING AGENTS
CHICKENS
EGTA
FILTRATION
ION EXCHANGE
MICROSOMES
PHOSPHATES
TRACER TECHNIQUES
ALCOHOLS
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIRDS
CALCIUM ISOTOPES
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CHARGED PARTICLES
DAYS LIVING RADIOISOTOPES
ENZYMES
ESTERASES
EVEN-ODD NUCLEI
FOWL
GLYCOLS
HYDROLASES
HYDROXY COMPOUNDS
INTERMEDIATE MASS NUCLEI
IONS
ISOTOPE APPLICATIONS
ISOTOPES
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANOIDS
OXYGEN COMPOUNDS
PHOSPHATASES
PHOSPHORUS COMPOUNDS
RADIOISOTOPES
SEPARATION PROCESSES
VERTEBRATES
550201* - Biochemistry- Tracer Techniques