A comparative study on the extraction of membrane-bound bilirubin from erythrocyte membranes using various methods

In this study, we used three different methods for the extraction of membrane-bound bilirubin (EMB) from erythrocyte membranes. Use of 2.5% albumin, pH 7.4, for elution of EMB resulted in only 34% of the total EMB which was estimated after the solubilization of bilirubin-loaded erythrocyte membranes (BLEMs) with 1% SDS. On the other hand, incubation of BLEMs with 38 mM sodium carbonate solution containing 5 mM EDTA, pH 11.0, yielded 77% of the total EMB. Application of Fog's reaction for the estimation of EMB directly on the BLEMs resulted in the estimation of 75% of the total EMB. These results suggest that either of the above methods, i.e. use of albumin or high pH, or direct Fog's reaction cannot estimate the total EMB correctly. Increase in ionic strength from 0.15 to 0.45 did not release any EMB from erythrocyte membranes. Therefore, the best method for the estimation of total EMB is the solubilization of membrane with 1% SDS followed by Fog's reaction method. (C) 1999 Elsevier Science B.V. All rights reserved.