Formation Of Calcium Phosphate Minerals Research Articles

A facilitative role for carbonic anhydrase activity in matrix vesicle mineralization

Carbonic anhydrase (CA) which catalyzes the reversible hydrolysis of carbon dioxide is known to be important in osteoclastic bone resorption, however, suggested roles in calcium phosphate mineral formation have not been previously demonstrated. Biochemical evidence is provided for the presence of CA in growth plate matrix vesicles (MV) and the level of activity determined by enzyme assay. Inhibition of CA activity with the specific inhibitor acetazolamide resulted in reduced rates of MV mineralization. Other inhibitor studies showed that MV mineralization was also impaired by 4,4-diisothiocyanatostilbene-2, 2-disulfonic acid (DIDS), a blocker of membrane bicarbonate channels. No evidence was found for the presence of any proton pumps or channels. When acetazolamide and DIDS were combined, their inhibitory effects on MV mineralization were additive. These findings suggest that MV posess a pH regulation system composed of carbonic anhydrase and a putative bicarbonate channel. This system may function in the MV by providing intraluminal buffering capacity. The control of intravesicular pH is important for the stabilization of the acid-labile nuclea-tional core complex and in preventing the build-up of protons during calcium phosphate phase transformations.

Intracellular mineralization of Bacterionema matruchotii.

Intracellular calcium phosphate mineral formation in Bacterionema matruchotii has been examined relative to two established points: the product of calcium and phosphorus levels at which spontaneous precipitation occurs (Ca x P), 50 (mg%)2, and the product at which calcium hydroxyapatite itself induces crystal growth, 35 (mg%) 2. The extent of intracellular mineralization in the defined calcifying medium was determined analytically after washing the cells. Electron micrographs of B. matruchotii cells revealed needlelike crystals of mineral, typical of calcium hydroxyapatite. Bacterionema matruchotii was found to be an efficient nucleator and can bring about the formation of solid phase at a Ca x P product as low as 35 (mg%)2.

Studies of Some Marine Phosphorites from Baja California: ABSTRACT

Along the western coast of Baja California, between approximately 24.5° and 27° N. lat., extensive fine-grained phosphate deposits occur on a 100-km.-wide continental shelf. They are found from a depth of 100 m. to the shore where carbonate apatite makes up to 25 per cent by weight of present and more ancient barriers built up in front of coastal lagoons. Their similarity with ancient phosphorites, believed to have developed on large shallow submarine platforms, prompted a study of these sediments. Intense seasonal upwelling of deep nutrient-rich waters from the California Current controls the hydrography of the whole shelf, and shallow ridges form an effective sill restricting circulation over it. A reducing environment has developed and iron sulfides are prese t nearly everywhere. Locally produced organic matter is being supplied continuously to the bottom through the oxygen-deficient waters, this at a fairly high rate because of shallow depths. Conditions favorable to the preservation of large quantities of non-oxidized inorganic phosphate in the sediments are in this way maintained. Whether or not this situation results in the present formation of calcium phosphate minerals cannot be ascertained. Apatite could be measured quantitatively by X-ray diffraction down to very low levels. This shows the persistence of a rich zone over 20-30 km. along the coast between depths of 60-100 m. From several evidences these deposits represent ancient barriers reworked during the last transgression. Onshore similar phosphatic sands over 50 ft. thick are kno n to exist in the vicinity of the lagoons. From geological considerations and geochemical arguments the average age of these deposits is Pliocene to Pleistocene. They could be as old as Miocene. They appear in equilibrium with their modern environment and, if so, could continue to develop, but unambiguous evidences concerning their present growth have been difficult to obtain. End_of_Article - Last_Page 1758------------