Folate throughout the serum is assayed playing with a great noncompetitive ligand joining radioassay

Folate throughout the serum is assayed playing with a great noncompetitive ligand joining radioassay

Folate (PteGlu) assay

In this assay, radiolabelled pteroylglutamic acid ([ 3 H] PteGlu; Amersham Pharmacia, Buckinghamshire, UK) was used as the tracer and methyl-HcuatroPteGlu (Sigma Chemical Co., St. Louis, MO, USA) as the unlabelled ligand and ?-lactoglobulin (Sigma Chemical Co., St. Louis, Mo, USA) as the binder. A typical reaction contained 0.2 mL of 0.05 M borate-Ringer’s buffer, pH 8.0 with ascorbic acid (2 mg/mL); 0.1 mL of methyl-H4PteGlu (50?300 pg) or 0.02 mL of serum sample and 0.1 mL of ?-lactoglobulin (binder that had been diluted to bind 50?60% of the tracer used in the assay) in a total reaction volume of 0.4 mL.

The reaction mixture was incubated at room temperature for 30 min and then the tubes were cooled to 4°C by placing them in an ice bath for 30 min. After this incubation, 0.1 mL of [ 3 H] PteGlu (200 pg) was added to each reaction tube and the incubation at 4°C was carried out for another 30 min. Then the reactions were stopped by adding 0.4 mL of cold 2.5% hemoglobin-coated charcoal. After thorough mixing, each reaction tube was subjected to centrifugation at 3000 rpm for 10 min at 4°C to pellet the charcoal. Radioactivity in the supernatant solution (0.5 mL) was counted in LS-6500 Spectrometer (Beckman Instruments, Palo Alto, CA, USA) using 5 mL of 3a70 scintillation fluor (Research Product International, USA). The standard dose–response curve was constructed by plotting the ratio of % [ 3 H] PteGlu bound (B) to % [ 3 H] PteGlu free (F) as a function of the amount of methyl-H4PteGlu in each standard.

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