Enzyme activity assay for horseradish peroxidase encapsulated in peptide nanotubes

Encapsulation of horseradish peroxidase (HRP) inside a peptide nanotube (PNT) was demonstrated and its activity was measured. Enzyme assay verified that 0.16 μg 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 HRP 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 °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.