A process based on orally-infected Rachiplusia nu larvae as biological factories for expression and one-step purification of horseradish peroxidase isozyme C (HRP-C) is described. The process allows obtaining high levels of pure HRP-C by membrane chromatography purification. The introduction of the partial polyhedrin homology sequence element in the target gene increased HRP-C expression level by 2.8-fold whereas it increased 1.8-fold when the larvae were reared at 27A degrees C instead of at 24A degrees C, summing up a 4.6-fold overall increase in the expression level. Additionally, HRP-C purification by membrane chromatography at a high flow rate greatly increase D the productivity without affecting the resolution. The V-max and K-m values of the recombinant HRP-C were similar to those of the HRP from Armoracia rusticana roots.