At moderately acidic pH values, the short chain fatty acid, caprylic acid, is an effective protein precipitant. It has found an application in immunoglobulin purification as conditions have been developed that result in the precipitation of the majority of non-immunoglobin proteins in the serum leaving the antibodies in solution. The concentration of caprylic acid required differs for the serum of different species as shown in Table 1 (see Note 12).
1. If necessary, clarify the serum by centrifuging at 3000g for 15 min at 4°C. Discard any precipitate and add 2X vol of 0.06 M sodium acetate, pH 4.0.
2. While stirring, add the required volume of caprylic acid (see Table 1) dropwise, then leave stirring for 30 min at room temperature.
3. Centrifuge at 3000g for 30 min at 4°C.
4. Carefully remove supernatant and discard the precipitate.
5. Dialyze the supernatant overnight at 4°C against a suitable buffer.
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