Recent use of transgenic plants as an alternative protein expression system offers the potential to recover native plant enzymes as byproducts from recombinant protein purification processes. From the perspective of reduced presence of like-charged, native matrix proteins, canola and corn would be favored hosts for acidic recombinant proteins, while soybean would be favored for basic ones. Hence, we have examined two established techniques in recombinant protein downstream processing, i.e. ion-exchange chromatography and polyelectrolyte precipitation, for their potential for enzyme byproduct recovery from plants viewed as hosts for recombinant protein production.Cation exchange chromatography of nontransgenic canola and soy extracts completely recovered native alpha-galactosidase and urease activities in the extract. alpha-Galactosidase and beta-glucosidase activities were fully recovered in anion exchange chromatography of corn germ proteins with enrichment factors of about 3. Simple anion exchange chromatography for canola extracts recovered alpha-galactosidase activity with 59% yield and I I times enrichment. Polyelectrolyte precipitation using polyethyleneimine at a dosage of 38 mg/g total protein recovered 47% of alpha-galactosidase from canola with an enrichment factor of about 3. Several recommendations on the utilization of the byproduct fractions are proposed. Additional processing of byproduct fractions to concentrate form appears economically feasible. (C) 2003 Published by Elsevier Inc.