We have characterized the folate receptor in malignant and benign tiss
ues of human female genital tract (Fallopian tube and benign and malig
nant tissues of uterus). Radioligand binding displayed characteristics
similar to those of other folate binding proteins. Those include a hi
gh-affinity type of binding (K = 10(10)M(-1)), apparent positive coope
rativity, a slow dissociation at pH 7.4 becoming rapid at pH 3.5, and
inhibition of binding by folate analogues. The gel filtration profile
of Triton X-100 solubilized tissue contained two large peaks of H-3-fo
late labelled protein (> = 130 and 100 kDa) as well as a 25 kDa peak.
Only a single band of 70 kDa was seen on SDS-PAGE immunoblotting. The
large molecular size forms on gel filtration appear to represent folat
e receptors having a hydrophobic membrane anchor inserted into Triton
X-100 micelles. The folate receptor of female genital tract showed cro
ss-reactivity in ELISA and positive immunostaining with rabbit antibod
ies against human milk folate binding protein. Variations in the ratio
of immunoresponse to total high affinity folic acid binding suggests
the presence of multiple isoforms of the receptor in different types o
f malignant and benign tissues.