The student researchers purified the enzyme beta-galactosidase from E. coli using several techniques. They first lysed the E. coli cells and isolated the crude lysate. Ammonium sulfate precipitation was used to precipitate proteins, with the 30-45% fraction exhibiting the highest beta-galactosidase activity. Ion exchange chromatography further purified the samples using a salt gradient. Affinity chromatography achieved additional purification by exploiting the enzyme's affinity for its substrate. Bradford and ONPG assays measured protein concentration and enzyme activity after each step. SDS-PAGE analysis confirmed the isolation of pure beta-galactosidase.