Abstract
Because of the complications introduced by the presence of proteins in serum, we studied first the solubility equilibria in protein-free solutions. We 1 found that, at the pH of serum, solutions with the inorganic composition of ricketic serum are markedly under-saturated with respect to CaHPO4. Solutions with the calcium and phosphorus content of normal blood serum are slightly undersaturated; it is only solutions which have Ca × P products greater than about 50 which are supersaturated with respect to CaHPO4.
Since part of the calcium in serum is bound to protein, it was predicated that ricketic serum is undersaturated with respect to CaHPO4; normal serum should be slightly undersaturated with respect to this substance.
This theory was tested by shaking blood sera for one hour at 38° with crystalline CaHPO4. As a result of the equilibration, the phosphorus increased in all cases; in some cases both calcium and phosphorus increased. In every case equilibration produced an increase in the Ca × P product and in the [Ca] × [HPO4”] product. In the sera as drawn, the Ca × P products ranged from 35 to 85, and the [Ca] × [HPO4”] products ranged from 2.4 × 10-6 5.7 × 10-6. The final Ca × P products ranged from 74 to 88; the final [Ca] × [HPO4”] products ranged from 5.3 × 10-6 to 6.5 × 10-6.
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