Folate binders in body fluids.
In normal serum, saline dialysis for 48 hours in Visking casing resulted in folate clearance closely comparable to that produced by haemoglobin-coated charcoal adsorption, except in kwashiorkor where charcoal removed a greater proportion of folate. Pre- and post-dialysis values probably represented total and bound folate, respectively. Urinary folate consisted almost exclusively of dialyzable or free folate. Folate in saliva, bile, and erythrocytes consisted of dialyzable and non-dialyzable fractions; gastric juice contained minimal amounts of folate. In spite of low serum albumin in kwashiorkor the bound folate fraction was increased rather than decreased; in myeloma with hyperglobulinaemia there was no increase in the bound folate fraction. Nephrotic urine did not contain excess folate, but pregnancy urine (third trimester) showed increased total folate.Serum, chromatographed on Sephadex G-25, produced two folate peaks, only the first being associated with serum proteins. Urine contained only a second folate peak corresponding to the elution peak of pteroyl-monoglutamic acid (PGA). Adsorption studies with charcoal coated with ;molecular sieves' of varying size suggested that the predominant serum folate binder was of molecular weight 70,000-120,000. It is unlikely to be albumin.