The Binding of Bilirubin to Agar 1

Abstract

Summary

The binding affinity of agar for bilirubin was measured in vitro by suspending agar in isotonic solutions of pH 7.9 containing concentrations of bilirubin between 0.017 to 1.4 mM. The affinity constant for bilirubin was 10⁵ and the number of binding sites (n = 0-55/5.0 × 10⁴g of agar) was dependent upon the calcium and sulfate contents of the agar. Calcium depleted agar had no affinity for bilirubin but regained its affinity by addition of calcium proportionate to the sulfate content. The number of moles of bilirubin bound by agar greatly exceeded the molar content of Ca²⁺ and SO^- ₄ and suggested that bilirubin was bound between the hydrophobic interstices of the cross-linked strands of agar. Water soluble organic anions did not show significant binding to agar.