A rapid and sensitive homogeneous enzyme-linked competitive binding assay for folate that exhibits unique dose-reponse characteristics is described. The method utilizes a highly substituted glucose 6-phosphate dehydrogenase-folate conjugate in conjunction with folate binding protein. In the absence of folate, the enzyme conjugate is inhibited up to 70 %. In presence of folate, activity is regained in an amount proportional to the folate concentration. Such reversal occurs over an extremely narrow concentration range and this range can be fine tuned to desired values by varying the concentration of folate binding protein and/or the enzyme-folate conjugate. Theoretical models suggest that this unusual behavior can be attributed to the favorable equilibrium constants between folate binding protein and conjugate. The new assay is shown to be precise, accurate, selective, and useful for the measurement of folate in vitamin preparations. Speculation as to the advantageous use of this novel assay in a yes/no type quality control situation is also presented.
ASJC Scopus subject areas
- Analytical Chemistry