Abstract
In animal experiments, variation was found between agar lots in their effect on fecal excretion of bile pigments and on lowering of serum bilirubin levels in the Gunn strain of rat. The binding of bilirubin to agar was studied in vitro to account for the variation. Suspensions of agar powder in bilirubin solutions (isotonic, 37°, pH 7.9) were employed to derive adsorption isotherms. From these, the association constants (Ka) for the binding reaction was about 2×105 for all products. The capacity for binding (n) varied between 25 and 56 moles of bilirubin/50,000 g. of agar. The variation in (n) was related to the calcium and sulfate content of the agar products. The calcium and sulfate content of the agar lots each varied from less than 1 to 11 moles/50,000 g. of agar. Calcium-depleted agar lost its bilirubin binding capacity and regained it upon readdition of calcium. Salicylate, sulfonamide, BSP and HABA dyes, and conjugated bilirubin were not bound by agar. Cellulose, phosphocellulose and DEAE-cellulose did not bind bilirubin as well as agar. Binding of bilirubin to agar decreased as pH, ionic strength, or urea concentration were independently increased. There was an increase in apparent Ka with a rise in temperature. Free energy change was about 2 kcal/mole. A model is proposed in which strands of carbohydrate are cross-linked with ionic calcium disulfate bridges to form relatively apolar interstices between chains and between bridges in which bilirubin is bound possibly by hydrophobic interaction or by hydrogen bonds or both.
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Poland, R., Odell, G. THE BINDING OF BILIRUBIN TO AGAR. Pediatr Res 8, 407 (1974). https://doi.org/10.1203/00006450-197404000-00404
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DOI: https://doi.org/10.1203/00006450-197404000-00404