Bone in dermatosparaxis. II. Chemical analysis

Physical and chemical analysis of the organic matrix of dermatosparactic (D-) bone was performed to evaluate the implication of an alteration in the mechanical properties of procollagen fibers in the process of calcification. The D-diaphyseal bone contained less collagen and more hydroxyapatite than normal (N-) calf bone. Fractionated by centrifugation in a density gradient, D-bone was found to be composed of more than 80% weight of a highly calcified fraction while N-bone of the same age contained only 37% of this fraction. As compared to N-bone, the amount of organic matrix per unit volume of D-bone was increased in the least calcified fractions and reduced in the most mineralized ones. The newly formed matrix of D-bone contained an amount of collagen similar to the N-bone while the concentration of other glycoproteins was higher. Calcification was accompanied, in both types of bone, by a progressive reduction of glycoproteins and collagen; the diminution of collagen was higher in D- than in N-bone. The presence in D-bone of procollagen fibers with altered mechanical properties might be responsible for an excess of glycoproteins in the newly formed matrix. Calcium salt deposition in this matrix and progressive distension of the fibrous framework are two possible mechanisms by which hypercalcification of D-bone occurs.