Isolation of a sulfobromophthalein binding protein from hepatocyte plasma membrane

This paper deals with the isolation and partial characterization of a protein capable of high affinity sulfobromophthalein-binding from liver plasma membrane. The purification involves acetone powder of a crude preparation of rat liver plasma membrane, salt extraction and purification through two chromatographic steps. Based on sulfobromophthalein binding, the process gives a yield of approximately 40%, with a purification of about 300 times with respect to the starting homogenate. The best preparation can bind more than 100 nmol sulfobromophthalein/mg protein. The protein behaves as a single species in dodecyl sulphate polyacrylamide gel electrophoresis, with an apparent molecular weight of 1.7 · 105. The molecule does not contain sugars. The dissociation constant of the protein · sulfobromophthalein complex has been found to be 4 · 10−6 M, a value in agreement with that of high affinity binding sites described on isolated liver plasma membrane.