Ca²⁺ binding properties of type X collagen

Type X collagen is a developmentally regulated collagen that is only synthesized by chondrocytes of the hypertrophic and calcifying zone in fetal cartilage. There is evidence in the literature that type X collagen may be involved in cartilage calcification. Here we show that type X collagen synthesis precedes calcium deposition in nodules of fetal human chondrocytes forming in cell culture and present evidence that type X collagen binds calcium in a specific and dose dependent manner. In an assay using bovine type X collagen coupled to beads and ⁴⁵Ca²⁺ we determined a total of about 15 binding sites per α1(X) chain with a dissociation constant of 32 μM.