PROTEIN-CONCENTRATION DEPENDENCE OF PALMITATE BINDING TO BETA-LACTOGLOBULIN

The binding of palmitate to beta-lactoglobulin at protein concentratio ns ranging from 1 to 200 mu M was determined using an ultrafiltration method with [C-14]palmitate. Fit of the data to theoretical models req uired the assumption of two independent sets of binding sites; however , binding characteristics were dependent on the protein concentration. A model assuming one set of sites on the protein monomer and another on the dimer was consistent with the data. The analysis suggests that 2 mol of palmitate are bound/mol of dimer and that the binding constan t is of the order of 10(5) M-1; a larger number of palmitate molecules are bound per mole of monomer with a smaller binding constant of the order of 10(4) M-1. Apparently, formation of the dimer, by hydrophobic interactions at the monomer contact site, eliminated palmitate bindin g sites on the monomer but formed a higher affinity pocket for binding to the dimer.