Matrices that Calcify

A variety of organic matrices are able to initiate or accelerate the precipitation of calcium and phosphate ions from solution (Strates et al., 1957; Santanam, 1959; Bachra et al., 1959; Bachra and Sobel, 1959a; Glimcher et al., 1957; Glimcher, 1960) by a process called heterogeneous nucleation (Neuman and Neuman, 1958; Glimcher et al., 1961a; Taves, 1963). Since mineral is normally deposited extra-cellularly, these observations may help to explain the manner in which the mineral phase of bone is formed and localized. Many of these studies were carried out with collagenous matrices in which the collagen fibers were highly ordered (Strates and Neuman, 1958; Glimcher et al., 1957; Fleisch and Neuman, 1961). Therefore, it has been proposed, in analogy with nucleation phenomena in inorganic chemistry, that such organization is a necessary characteristic of a template which can influence the rate of crystal formation (Neuman and Neuman, 1958; Glimcher, 1960; Solomons et al., 1960; Glimcher et al., 1961a). In man, mineral is found associated with at least three clearly different protein matrices: bone collagen, the enamel protein, and aortic elastin. In the cases of collagen and enamel protein, calcification proceeds as a step in normal tissue development, although the process may vary with each matrix. The mineralization of elastin occurs later in life and appears to be a pathological process.