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Identification of an Immunoreactive Folate in Serum Extracts by Radioimmunoassay *
Author(s) -
DaCosta Maria,
Rothenberg Sheldon P.
Publication year - 1971
Publication title -
british journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.907
H-Index - 186
eISSN - 1365-2141
pISSN - 0007-1048
DOI - 10.1111/j.1365-2141.1971.tb03422.x
Subject(s) - radioimmunoassay , vitamin , folic acid , chemistry , antibody , endocrinology , biochemistry , dihydrofolate reductase , medicine , enzyme , immunology
S ummary . A radioimmunoassay for folic acid using antibodies with binding determinants specific for this vitamin has been used to identify an immunoreactive folate in serum and serum extracts. Because reduced folates such as methyltetra‐hydrofolate, formyltetrahydrofolate and dihydrofolate did not inhibit the antibody binding of [ 3 H]folic acid while unreduced folates did, the immunoreactive folate in serum and serum extracts was most likely an unreduced folate. Serum extracted by boiling in the absence of ascorbate had a significantly higher concentration of immunoreactive folate than did whole serum. The extraction procedure apparently released or converted endogenous folate to an immunoreactive form because serum extracted with ascorbate contained very low concentrations of the immunoreactive form. The range of recovery of crystalline folic acid added to serum and assayed in extracts prepared without ascorbate was 82‐132%, with a mean of 104%. Subjects taking oral folic acid had significantly elevated levels of serum immunoreactive folate. Following intravenous administration of folic acid, the immunoreactive folate concentration did not rise as high and it decreased more rapidly in folate deficient patients than in normal subjects. Serum extracted without ascorbate from normal, vitamin B 12 and folate deficient subjects had immunoreactive folate levels (mean ± SEM) of 1350 ± 110, 949 ± 152 and 525 ± 72 pg/ml, respectively.