A study on the use of caprylic acid and ammonium sulfate in combination for the fractionation of equine antivenom F(ab')(2).

This study involved the fractionation of equine antivenom F(ab')(2) by combined stepwise ammonium sulfate (AS) and caprylic acid (CA) precipitation without intermediate separation of precipitate. Using a microplate format, 55 conditions with combinations of AS (0-20% saturation) and CA (0-5% v/v), were tested. AS significantly reduced the turbidity raised by CA. High specific antibody activity was observed in the area containing 2-5% CA and 10-20% AS. From these results, 12 precipitation conditions were selected for detailed quantitative studies. Two combinations, one with 4% CA and 15% AS and another with 5% CA and 20% AS, gave the highest fold-purification (1.79 and 1.83) with antibody recoveries at 68% and 59%, respectively. These combinations offered a benefit over CA alone in reducing the turbidity and in increasing the purity but not the recovery of antibody. The conditions giving more favorable overall results were with 2% CA alone and another with a combination of 1.5% CA and 10% AS. These preparations of F(ab')(2) were homogeneous and without protein aggregate under size-exclusion HPLC. Lastly, 1 h precipitation showed better results than those of overnight precipitation. These results could be useful for the production of therapeutic antivenoms.