Biochemical and immunohistochemical evidence that in cartilage an alkaline phosphatase is a Ca2+-binding glycoprotein.

Abstract

A glycoprotein that exhibits alkaline phosphatase activity and binds Ca2+ with high affinity has been extracted and purified from cartilage matrix vesicles by fast protein liquid chromatography. Antibodies against this glycoprotein were used to analyze its distribution in chondrocytes and in the matrix of calcifying cartilage. Under the light microscope, using immunoperoxidase or immunofluorescence techniques, the glycoprotein is localized in chondrocytes of the resting zone. At this level, the extracellular matrix does not show any reaction. In the cartilage plate, between the proliferating and the hypertrophic region, a weak immune reactivity is seen in the cytoplasm, whereas in the intercolumnar matrix the collagen fibers appear clearly stained. Stained granular structures, distributed with a pattern similar to that of matrix vesicles, are also visible. Calcified matrix is the most stained area. These results were confirmed under the electron microscope using both immunoperoxidase and protein A-gold techniques. In parallel studies, enzyme activity was also analyzed by histochemical methods. Whereas resting cartilage, the intercellular matrix of the resting zone, and calcified matrix do not exhibit any enzyme activity, the zones of maturing and hypertrophic chondrocytes are highly reactive. Some weak reactivity is also shown by chondrocytes of the resting zone. The observation that this glycoprotein (which binds Ca2+ and has alkaline phosphatase activity) is synthesized in chondrocytes and is exported to the extracellular matrix at the time when calcification begins, suggests that it plays a specific role in the process of calcification.

Differential Expression and Activity of Tissue-nonspecific Alkaline Phosphatase (TNAP) in Rat Odontogenic Cells In Vivo

“…activity in enamel and dentin were identical, in contrast with cartilage, where the protein detected was either enzymatically inactive or active in the extracellular compartment, depending on the stage of biomineralization (De Bernard et al 1986). In bone, TNAP protein was not associated with a distinct extracellular structure, as described previously (Pinero et al 1995).…”

“…In contrast, the cells of the follicular sac surrounding the forming rat incisor react with the TNAP antibodies (FS). Bar ϭ 12.2 m. Kurahashi and Yoshiki 1972;Deporter and Ten Cate 1976;Linde and Granström 1980;Orams and Snibson 1982;De Bernard et al 1986;Takano et al 1986;Bonucci et al 1992;Gomez and Boyde 1994;Linde and Lundgren 1995;Wöltgens et al 1995). TNAP immunolabeling has been previously performed during the first steps of amelogenesis and dentinogenesis (Hoshi et al 1997), whose data are consistent with our study.…”

Antiosteoporotic effect of Coelatura aegyptiaca shell powder on ovariectomized rats

“…Furthermore, the increased level of BALP in CES treated group may be attributed to the increased levels of Ca and P contents in bone (Buckwalter and Cooper, 1987). Debernard et al (1986) reported that BALP could act as a plasma membrane transporter for inorganic phosphate, or an extracellular calcium-binding protein that stimulates calcium phosphate precipitation and orients mineral deposition into osteoid. BALP may also be involved in the mineralization process by hydrolyzing organic phosphates to release free inorganic phosphorus at sites of mineralization (Mori-Okamoto et al, 2004).…”

Micronutrients and longitudinal growth

“…ALP has long been associated with mineralization and inhibition of ALP impairs calcification (Register & Wuthier, 1984), although its exact role is unclear. Active ALP is found only in the mineralizing and pre-mineralizing chondrocytes (de Bernard et al 1986;Farquharson et al 1992c) suggesting that activation is a key event during calcification.…”