THE NATURE OF CIRCULATING ESTROGEN:LIPOPROTEIN-BOUND ESTROGEN IN HUMAN PLASMA12

Abstract
Direct assay of the purified protein fractions of human plasma, as prepared by Cohn et al. (1946), revealed that practically all of the protein-bound estrogen present occurs in the lipo-protein fraction III-O. The estrogen dialyzed readily out of (his fraction under simulated physiologic conditions. Evidence was presented that the estrogen in fraction III-O may be estriol, and that it is attached to the protein in an esterified form. The physico-chemical characteristics and physiologic significance of the estrogen-protein complex have been discussed.