BINDING OF BILIRUBIN TO ERYTHROCYTES FROM DIFFERENT MAMMALIAN-SPECIES

The binding of bilirubin to erythrocytes of several mammalian species, i.e. human, buffalo, goat and sheep was studied. In all cases, curves between bilirubin desorbed from erythrocytes and bilirubin in the inc ubate followed Michaelian saturation kinetics. The dissociation consta nts of the bilirubin-receptor complex and saturable binding sites were calculated using double reciprocal plots. Goat erythrocytes had the h ighest dissociation constant (265.7 mu mol/l) and highest saturation ( 125.9 mu M), whereas sheep erythrocytes had the lowest dissociation co nstant (115.6 mu mol/l) and lowest saturation (62.5 mu M). Buffalo and human erythrocytes bound bilirubin in a similar fashion, and the valu es of interaction parameters were midway between those obtained with g oat and sheep erythrocytes. Differences in the affinity and number of saturable binding sites can be attributed to the different make-up of the erythrocyte membranes of these species.