Role of serum folate binders in the delivery of folate to tissues and to the fetus.

Specific folate binding protein (FBP) and non-specific binding protein have been prepared from pooled serum from patients in late pregnancy. The two classes of folate binder were labelled with 75Se-selenofolate and injected into non-pregnant and pregnant rabbits. Selenofolate bound to specific FBP was delivered predominantly to the liver, in both pregnant and non-pregnant animals. Fetal tissue took up selenofolate from non-specific FBP only. Specific FBP thus functions to deliver folate to stores and represents a storage pool of folate. The non-specific FBP are responsible for the delivery of folate to the fetus, and probably also to sites of utilization.