The Phosphatase Activity of Tissues and Plasma in Tumors of Bone

Robison, in 1923 (22), suggested that phosphatase plays an important role in the formation of bone in the human body. He found a very active phosphatase in preparatory areas of ossification, and held that this enzyme hydrolyzed the phosphoric esters in the blood to bring about a local increase in the concentration of the phosphate ions. It was his theory that the solubility product of tertiary calcium phosphate was thereby exceeded, and that deposition of this salt therefore occurred in the ossifying zone. Evidence has since accumulated, chiefly through the work of Robison and Kay and their associates, to strengthen this hypothesis and to make it the most satisfactory modern theory of the deposition of calcium salts in zones of ossification. It has been demonstrated: ( a ) that, in bones, deposition of calcium salts occurs in vitro in zones of preparatory ossification, in the periosteum, and in the regions occupied by the enlarged cartilage cells (23); ( b ) that small amounts of phosphoric esters, hydrolyzable by bone phosphatase, are present both in red blood corpuscles (15) and in blood plasma (18); ( c ) that membrane-bone as well as cartilage-bone synthesizes phosphatase while growing in tissue culture (7); ( d ) that phosphatase is not present in any cartilage prior to the appearance of a center of ossification (17); ( e ) that it fails to appear in non-ossifying cartilages such as Meckel's cartilage, rib cartilage, and tracheal cartilage (6, 7); ( f ) that the enzyme is found wherever active ossification is taking place, and is present in greatest amounts in bone at the time when the deposition of calcium salts is most active (17); ( g ) that the periosteum and the enlarged cartilage cells of the metaphysis of embryo and infant bones are very rich in phosphatase, while the epiphysis beyond the zone of active ossification is comparatively deficient in the enzyme (16, 17, 19).