Calcium-Phospholipid-Phosphate Complexes in Mineralizing Tissue

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Abstract
Ca-phospholipid-phosphate complexes were isolated from mineralized tissues using a sonication-dependent method described previously and a new method which depends on the use of enzymes to remove the nonlipid matrix from tissues which were decalcified under mild conditions. Both methods gave comparable results. The complexes were found to be constituents of all mineralized rabbit tissues; bone, calcified cartilage and tooth. No such complexes could be isolated from the nonmineralized tissues; muscle, ear cartilage, bone marrow, adipose tissue. The proportion of Ca-PL-PO4 is highest in those tissues which are involved in active mineralization, i.e., the younger tissues. All complexes isolated from mineralized tissues contain 50 mol % Ca, and variable amounts of the acidic phospholipids and inorganic phosphate. The Ca:total P molar ratio was always unity. All isolated complexes were shown to induce in vitro hydroxyapatite formation from metastable calcium phosphate solution and are believed to be associated with in vivo calcification.