Molecular Pharmacology, Vol 12, 454-462, Copyright © 1976 by the American Society for Pharmacology and Experimental Therapeutics

The Extent of Hydrophobic Binding Area Studied by Fatty Acid Binding to Albumin

¹ Departments of Pharmacology and Biophysical Chemistry, University of Nijmegen, Nijmegen, The Netherlands

Affinity constants of six consecutive fatty acids, propionic to caprylic, for the specific binding site on albumin have been determined at two temperatures. The standard free energy change of binding, G°, deduced from the affinity constants, appears not to increase linearly with increasing chain length; a plateau is reached at valeric acid, and G° increases further only at heptanoic acid. The mean increment in G° per methylene group amounts to 820 cal, indicating that the hydrophobic interaction of the alkyl chain of the fatty acid with the specific binding site is quite optimal. The occurrence of the plateau has been interpreted as being a consequence of the limiting extent of the hydrophobic binding area forming part of the specific binding site for fatty acids on albumin. As the position of the plateau seems to coincide with that in other work, using other systems, the limiting extent of the hydrophobic binding area might be a general feature of proteins.

Note:
ACKNOWLEDGMENTS The authors are indebted to Professor Dr. E. J. Ariëns for helpful suggestions and criticism in this study. We gratefully acknowledge the experimental assistance of Mr. A. C. Wouterse and the skillful construction of an improved dialysis apparatus by Mr. J. A. L. Janssen, as well as the indispensable assistance of Drs. M. A. van’t Hof in applying the computer curve-fitting procedure.