INVOLVEMENT OF LYSINE RESIDUES OF GOAT SERUM-ALBUMIN IN HIGH-AFFINITYBINDING OF BILIRUBIN

Four maleylated derivatives of goat serum albumin having percent modif ication as 40%, 46%, 84% and 98% were prepared using varying molar rat io of maleic anhydride over protein. These preparations were found to be pure, both with respect to size and charge as judged by gel filtrat ion and polyacrylamide gel electrophoresis. Maleylation caused signifi cant change in protein conformation as revealed by the change in Stoke s radius and frictional ratio of serum albumin, from 3.46 nm and 1.28 to 4.96 nm and 1.79, respectively, upon 98% modification. Immunodiffus ion results of native and modified albumins with anti-goat serum album in antiserum also suggested significant conformational changes in seru m albumin upon maleylation. About 88% reduction in bilirubin binding w as observed after modification of 98% amino groups of serum albumin as studied by visible difference spectroscopy at pH 8.0, and at 0.15 ion ic strength. Increase in ionic strength to 1.0 did not lead to any sig nificant reversal in bilirubin binding. These results prove the involv ement of lysine residues in bilirubin-albumin interaction.