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 incubate followed Michaelian saturation kinetics. The dissociation constants of the bilirubin-receptor complex and saturable binding sites were calculated using double reciprocal plots. Goat erythrocytes had the highest dissociation constant (265.7 mumol/l) and highest saturation (125.9 microM), whereas sheep erythrocytes had the lowest dissociation constant (115.6 mumol/l) and lowest saturation (62.5 microM). Buffalo and human erythrocytes bound bilirubin in a similar fashion, and the values of interaction parameters were midway between those obtained with goat 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.