Calcification. XXIV. Mineralization of collagen and other fibers

Abstract Purified tail tendon and skin acid-soluble collagens mineralize equally well in vitro when precipitated with chondroitin sulfate. Crude preparations of skin collagen mineralize poorly, compared to tail tendon collagen. Finely cut rat tail tendon showed appreciable calcifiability in vitro , but fresh skin calcified only to a slight extent. Fibrin, in some experiments, and, to a small extent, surgical silk calcified in vitro . Rat hair and filter paper did not calcify in vitro . Acid-insoluble (often referred to as cross-linked) bovine Achilles' tendon collagen and rachitic bone slices treated with 0.5 M sodium citrate at a pH of 7.3 calcified in vitro , but this calcifiability was blocked by acidification or EDTA. Calcification in vitro of rachitic cartilage takes place at a more rapid rate and a lower Ca × P product than that of collagen. Some objections to the collagen concept of mineralization are presented. It is concluded that although the mineralization of collagen represents an incomplete or inadequate model for the mineralization of calcifying matrix in vivo , it does constitute a mineralizing matrix related to bone.