BINDING OF ELLIPTICINE TO BETA-LACTOGLOBULIN - A PHYSICOCHEMICAL STUDY OF THE SPECIFIC INTERACTION OF AN ANTITUMOR DRUG WITH A TRANSPORT PROTEIN

The unprotonated form of the anti‐tumor alkaloid ellipticine binds to β‐lactoglobulins A and B from bovine milk with an affinity constant of 7 ± 3 × 105 M−1. There is one binding site/dimeric protein molecule (the stable form at medium pH). The attachment site is not the β‐barrel nor the hydrophobic site identified as the retinol site in β‐lactoglobulin but a domain located at the interface of the two monomeric units where the ligand lies close to Trp61 of both polypeptide chains. The positive binding enthalpy observed in temperature‐jump relaxation experiments is overcome by a strong entropy increase, tentatively thought to result from water release at the binding domain. Accordingly, desolvation is assumed to be the rate‐determining step in the process of ellipticine binding. Copyright © 1990, Wiley Blackwell. All rights reserved