THERMODYNAMIC APPROACH TO THE SELECTION OF POLYURONIDE SEQUESTRANTS FOR PREVENTIVE AND MEDICINAL NUTRITION

An approach to the analysis of isotherms of cooperative binding is dev eloped that allows to calculate approximately affinity profiles, i.e. dependencies of binding constants on binding densities. The comparison of the affinity profiles of the interactions of Ca2+ and Sr2+ ions Wi th sodium pectate as well as sodium alginates with the different conte nt of the blocks of alpha-L-guluronic acid residues (GG-blocks) and bl ocks of mixed composition showed that (1) pectate has higher affinity to both ions as compared with alginates; (2) the affinity of pectate t o Ca2+ ions is comparable to its affinity to Sr2+ ions but in the case of Ca2+ ions the maximum of the affinity profile falls on the substan tially lesser value of the binding density in comparison to Sr2+ ions that seems to be unfavorable from the standpoint of the use of this po lyuronide in preventive or medicinal nutrition; (3) the affinity of bo th alginates to Sr2+ ions at relatively low binding densities exceeds their affinity to Ca2+ ions; (4) the affinity of alginates to Sr2+ ion s increases with the increase in the content of GG-blocks, whereas the affinity to Ca2+ ions practically does not depend on the composition of the alginate; (5) the maximum binding density of Sr2+ ions to the a lginates approximately corresponds to the content of GG-blocks. These results corroborate the practice of the use of alginates rich in resid ues of alpha-L-guluronic acid for the removal of radioactive strontium from the digestive tract. The binding constants of Pb2+ ions to pecta te over a wide range of binding densities are more than an order of ma gnitude greater than those of alkali-earth metal ions.