Bitter melon seeds were obtained from the Institute of Agricultural Science and Technique of Sichuan Province, China. Matrices for electrophoresis were products of Sigma-Aldrich (St Louis, MO) and Bio-Rad Laboratories (Hercules, CA). SP-Sepharose FF, Sephacryl S-100, Macro-Cap-SP, and ampholyte were purchased from Amersham Pharmacia Biotech (Piscataway, NJ). (mPEG) 2 -Lys-NHS (20 kDa) was obtained from Shearwater Polymers (Huntsville, AL). Dulbecco's Modified Eagle's Medium (DMEM) and fetal bovine serum used in cell culture were from Gibco BRL (Grand Island, NE). pUC18 DNA was purchased from TAKARA (Dalian, China). Nitrocellulose (NC) membrane was obtained from Bio-Rad Laboratories. Sheep-antimouse Ab-linked to alkaline phosphatase was purchased from Sigma-Aldrich. JAR choriocarcinoma cells were purchased from the Cell Bank of Shanghai Institute of Cell Biology (Shanghai, China).