High affinity of nonesterified polyunsaturated fatty acids for rat alpha-fetoprotein (AFP)

We have recently demonstrated that a mixture of nonesterified long chain fatty acids, mainly polyunsaturated, which are extracted under certain conditions from either whole mammalian sera or from pure rat alpha 1-fetoprotein (AFP), interfere with rat AFP-estrogen interaction. We present here a quantitative study of the association constants for the binding to AFP of these different fatty acids. We show important differences among them, the polyunsaturated ones displaying higher association constants (Ka approximately 10(7) -- 10(8) M-1) than the monounsaturated (Ka approximately 10(6) M-1) or the saturated (Ka approximately 10(4) -- 10(5) M-1) compounds. Moreover, though all the fatty acids identified in rat serum or rat AFP extract are more or less tightly bound by rodent AFP, only some of them can compete for exogeneous estrogens complexed to this highly estrophilic macromolecule.