ABSTRACT

This chapter provides substantial evidence that proteoglycans are topographically concentrated at sites of calcification. The focal concentration of proteoglycans, moreover, may also reflect an important supportive role for these macromolecules by providing an organic backbone which contributes to the growth and stability of the mineral phase. The dye stabilization techniques which we have described, when used in conjunction with high-resolution electron microscopy, identified a clearcut topographical relationship between proteoglycans and mineral. It will likely be some time before the biochemical properties of these specific proteoglycans are analyzed, and their precise function or functions fully ascertained. Finally, and possibly in combination with other functions, a condensation of proteoglycans may increase the local diffusion and flux of matrix constituents around proteoglycan-mineralizing sites. Ruthenium red and alcian blue both resulted in granular deposits, whereas the lower-molecular-weight dyes of safranin 0 and acridine orange stabilized proteoglycans as extended filamentous structures.