The objective of this research is to obtain a basic understanding of the mechanisms by which organic matrix controls biomineralization by studying the biochemical, physicochemical and structural aspects of the mineralization of collagen. The capacities of acidic macromolecules to induce mineral formation and to control mineral growth, and effects of collagen structure on localization and growth patterns of the mineral will be examined. The structural relationships between collagen, mineral and polyanions and changes in the collagen cross-links and three-dimensional fibrillar structure associated with the transition from non-mineralized to mineralized collagen in the calcifying turkey leg tendon will be detailed. The results will provide basic information about the mechanisms of biomineralization; information that is essential to developing therapies for basic skeletal disorders where matix control may be lost, such as osteoporosis and osteopetrosis. The capacities of immobilized acidic macromolecules to induce mineral will be determined from the mineral induction times and growth rates in a constant composition chemostat so that the comparisons are made on a kinetic basis. Control by the substrate will be investigated by attaching the polyanions to three genetically different collagens; types I, II, and X. Control of mineral growth will be examined by determining face-specific adsorption of fluorescently labelled polyanions onto hydroxyapatite crystals and the effect of this adsorption on the growth and habits of the crystals. This control also will be examined with polyanionicinduced mineral formation in a chemostat. The crystal types, their and the polyanions' localization with collagen structure will be determined by the use of specific electron microscopic (EM) imaging techniques, electron diffraction, image analysis, and 3D tomographic reconstruction. These EM techniques and specific histochemical stains and immunolabelling will be used to determine relationships between collagen fibrillar structure, mineral, proteoglycans and other polyanions and to compare the differences between the outer non-mineralizing portion in the inner mineralizing portion of turkey leg tendon and to determine changes in the inner portion of the tendon during the transition from a non-mineralized to a mineralized matrix Changes in the structure of the type I collagen in turkey leg tendon during the transition from a non-mineralized to a mineralized matrix will be studied by quantifying the molecular distribution of the covalent intermolecular cross-links and their precursor aldehydes in the collagen fibrils. This will be done by quantitative analysis of these compounds and determination of their molecular loci within the fibril by isolating these peptides from the tritiated sodium borohydride-reduced tissue. From this data, the specific three-dimensional structural changes of collagen fibrils associated with mineralization will be derived. The major phosphoproteins of this tissue, potential nucleators for mineralization, present will be isolated and characterized using ion exchange chromatography and phosphate and amino acid analyses.
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