The overall goal of this research is: (1) to identify intermediate calcium carriers which have a common mineralizing function in distantly related organisms, (2) to determine whether or not the carriers are derived from a common ancestral gene (3) to characterize the mineral-binding domains of the intermediate carriers, and (4) to determine how carrier-bound calcium ions are utilized to form a crystalline mineral phase. The specific aims for this proposal are: I. To demonstrate that phosphophoryn sequesters calcium phosphate in protected domains which are stable in the extracellular environment. II. To demonstrate that the bivalve hemocytes produce large quantities of native phosphoprotein particles. III. To isolate and characterize the coccolithisomes from the unicellular alga Hymenomonas carterae. IV. To determine the primary structure of phosphoprotein particles and identify any sequences homologous to the dentin phosphoprotein. Phosphophoryn, phosphoprotein particles, and coccolithisomes are the high- capacity calcium carriers in vertebrate dentin, molluscan bivalves, and unicellular algae, respectively. Ligand-binding studies are used to characterize the calcium phosphate sequestering domains in phosphophoryn. Cellular synthesis of native phosphoprotein particles is examined by immunocytochemistry and in vivo and in vitro translation of mRNA. Coccolithisomes are isolated by subcellular fractionation and ion exchange, molecular sieve, and affinity chromatography. Then the algal calcium carriers are characterized by amino acid and carbohydrate analysis. The primary structure of the phosphoprotein particles is determined from the nucleotide sequence of the cDNA. This project examines universal mineralization mechanisms applicable to normal skeletal and pathological calcification processes.