Encapsulation of horseradish peroxidase (HRP) inside a peptide nanotube (PNT) was demonstrated and its activity was measured. Enzyme assay verified that 0.16 mu g of the enzymes were encapsulated in 1 mg of PNTs. The encapsulation was also verified with TEM, UV-vis spectroscopy, and FTIR. The activity of the encapsulated H RP was examined for thermal stability, long-term storage stability, and resistance to a denaturant. They showed good storage stability, retaining its activity up to 90%, while the free HRP lost 50% of its activity over the course of 18 days. At 55 degrees C. the encapsulated HRP activity remained 20% higher than that of the free HRP. With the denaturant, guanidinium hydrochloride (GdmHCl), the encapsulated HRP activity was maintained around 10% higher than the free HRP. This result proves that the encapsulation of HRP inside the PNT may be an effective way to keep the enzyme activity stable in various environments. (c) 2012 Elsevier Inc. All rights reserved.