Serum Ca⁺⁺-Activity and Complexation

Abstract

Based on a general description of its most characteristic biological properties, we can say that calcium is a semimobile and hence a moderately fast exchanging cation. According to its property of forming moderately strong complexes of the oxygen-anion binding type with large anions, often after loss of its water of hydration, calcium acts as a structure forming and triggering cation. As we know, the chemistry and biological activity of calcium can be traced back to fundamental properties of this cation such as ion size, electron affinity, and geometric demand. It has previously been shown that in biological systems the sites of metal action are extremely selective with regard to cation diameter, are sensitive to changes in electron affinity of the cation, and are critically dependent upon stereochemistry. It is a reasonable hypothesis that the calcium binding sites in biological systems are gegenerally multi carboxylate or -phosphate centers (5). There is a strong indication that the activity of calcium ions in serum itself depends mainly on the cooperative interaction of ionized calcium on one side and primarily protein on the other. Other complexing agents are of minor importance.