Journal of Lipid Research, Vol. 19, 841-849, September 1978
Copyright © 1978 by Lipid Research, Inc.

The binding isotherms for the interaction of 5-doxyl stearic acid with bovine and human albumin

Selwyn J. Rehfeld , Delbert J. Eatough , and William Z. Plachy

Veterans Administration Hospital and Department of Laboratory Medicine, University of California, San Francisco, CA 94121; Thermochemical Institute, Brigham Young University, Provo, UT 84602; and Department of Chemistry, San Francisco State University, San Francisco, CA 94132

Binding isotherms for the interaction of 5-doxyl stearic acid with bovine and human albumin are reported. The critical micelle concentration (CMC) and the limiting solubility of 5-doxyl stearic acid were determined using the electron spin resonance (ESR)-spin label method. The CMC and the limiting solubility of this spin-label stearic acid in saline-phosphate buffer are 3.5 x 10^-5 M and 2 x 10^-4 M, respectively. We found no ESR line width evidence for pre-association of the spin-label stearate below the CMC. Maximum binding of the spin-label stearate to both bovine and human albumin occurs before micelle formation. The binding isotherm for spin-label stearic acid interaction with bovine albumin is in agreement with data obtained by others using [1-¹⁴C]stearic acid. For human albumin, comparison is difficult since previous data obtained with [1-¹⁴C]stearic acid vary widely. Comparison of the ESR 2T_|| values (the splitting between low and high field extremes, a measure of the degree of immobilization of protein-bound spin-label stearate) for bovine and human albumin indicates a greater immobilization of the spin-label molecules bound to human albumin. The binding data indicate that complexes are formed with bound spin-label stearate/albumin ratios of at least 18. The computed equilibrium constants for both bovine and human albumin indicate that the first seven spin-label molecules are tightly bound, log K > 5.0. The species predicted to form in solution by these equilibrium constants are reported.

Supplementary key words critical micelle concentration • electron spin resonance • equilibrium constants • binding sites • arginine • hydrophobic interactions

Submitted on September 12, 1977
Accepted on March 10, 1978

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				K. M. Cawthern, M. Narayan, D. Chaudhuri, E. A. Permyakov, and L. J. Berliner Interactions of alpha -Lactalbumin with Fatty Acids and Spin Label Analogs J. Biol. Chem., December 5, 1997; 272(49): 30812 - 30816. [Abstract] [Full Text] [PDF]