The Relative Binding of Calcium and Strontium with Serum Proteins and Other Substances

Sera from various mammalian species, solutions of various fractions of serum proteins, and solutions of certain other substances were tested by ultrafiltration in the presence of Ca⁴⁵ and Sr⁶⁵ for their binding of Ca, and Sr. For 6 species, human, dog, horse, cow, sheep, and rat, the ratio, Ca bound/Sr bound, was 1.29, 1.14, 1.19, 1.15, 1.17, and 1.13, respectively. The absolute degree of binding shown by these species falls into 2 groups. The human, dog, and horse sera bound the 2 ions to a lesser extent, 57% Ca and 47% Sr; cow, sheep, and rat sera bound the ions to a greater extent, 69% Ca and 60% Sr. Ultrafiltration of various serum protein fractions of the human and bovine revealed that fraction V (albumin) showed no difference between the binding of Ca and Sr but differences were noted with the globulin fractions (IV, III, II) that could account for the discrimination observed in whole serum. Results of the ultrafiltration of a variety of other proteins and polyelectrolytes led to the speculation that mucoproteins in the serum globulins could account for the large fiuctuations in binding of both ions by globulin fractions of various species; however, the results did notmore » show any indication of the type of substance or chemical grouping which could account for the slight but persistent discrimination between Ca and Sr that has been observed in whole serum. (auth)« less