GAD was incubated with the resin (1–10 mL) at a concentration of 5–10 mgGAD/mLresin for 1 h at room temperature in a binding buffer containing 20 mM sodium phosphate and 500 mM sodium chloride, pH 7.2, and GAD-immobilized resin was centrifuged at 300 rpm for 5 min and washed with the binding buffer three times.