Detergent activation of the binding protein in the folate radioassay
Hansen, S.I.; Holm, J.; Lyngbye, J.
Clinical Chemistry 28(1): 117-118
1982
ISSN/ISBN: 0009-9147 PMID: 7055893 Document Number: 183101
A minor cow's whey protein associated with .beta.-lactoglobulin is used as binding protein in the competitive radioassay for serum and erythrocyte folate. Seeking to optimize the assay, the performance of binder solutions of increasing purity was tested. The folate binding protein was isolated from cow's whey by means of CM-Sepharose CL-6B cation-exchange chromatography, and further purified on a methotrexate-AH-Sepharose 4B affinity matrix. In contrast to .beta.-lactoglobulin, the purified protein did not bind folate unless the detergents cetyltrimethylammonium (10 mmol/l) or Triton X-100 (1 g/l) were present. Such detergent activation was not needed in the presence of serum. There seems to be a striking analogy between these phenomena and the well-known reactivation of certain purified membrane-derived enzymes by surfactants (lipids/detergents).