constant stirring at 4 C to achieve an initial 30% saturation. After centrifugation at 9000 rpm for 15 min,
the precipitates were discarded and the supernatant was subsequently adjusted to 70% saturation with the addition of appropriate amounts of ammonium sulfate and the precipitates were dissolved in 20 mL 0.05 M glycine NaOH buffer (pH 8.0)