A high-affinity folate binding protein in fluid of benign cysts of human liver and mammary gland.

The presence of a folate binding protein in fluid of benign cysts of human liver and mammary gland was demonstrated. Radioligand binding was of a high-affinity type (K approximately 10(10) M -1). The gel filtration profile of cystic fluid contained two peaks of radiolabelled folate, a large one of 25 kDa and a small one of 100 kDa. The concentration of radioligand bound protein in samples of cystic fluid ranged from nil to 6 nM. In most cases the protein immunoreacted with antibodies against human milk folate binding protein. The data suggest that fluid of human liver and mammary gland cysts contains a folate binding protein which appears to be homologous to human milk folate binding protein.