Granzyme K is a member of the granzyme family of the serine proteases found specifically in the cytotoxic granules of cytotoxic T?lymphocytes (CTL) and natural killer (NK) cells. Human granzyme K is synthesized as a precursor (264?residues) with a signal peptide (residues 124), a propeptide (residues 25-26) and a mature chain (residues 27-264). The purified recombinant human Granzyme K consists of residues 27 to 264 which activity was measured by its ability to cleaves a thioester substrate Z-Lys-SBzl?HCl. The reaction was performed in 0.05 M Tris, 0.15 M NaCl, 0.01% Triton X-100, pH 8.0 (assay buffer), initiated by addition 50 μL of various concentrations of GZMK (diluted by assay buffer) to 50 μL of 1.2 mM substrate and DTNB mixture. The final well serves as a negative control with no GZMK, replace with 50 μL assay buffer. Incubated at 25℃ for 5min, then read at a wavelength of 405 nm. The specific activity of recombinant human Granzyme K is >220 pmol/min/μg.