Variant Cathepsin L Activity from Gastric Cancer Tissue

Cathepsin L activity was partially purified by S‐Sepharose FF chromatography, concanavalin‐A Sepharose chromatography, phenyl‐Superose column chromatography, Mono S column chromatography, and TSK G3000SWXL column chromatography from gastric cancer tissue. The optimal pH of cathepsin L from gastric cancer tissue was 7.4, and the activity was retained even at alkaline pH. Heat stability tests showed that cathepsin L from gastric cancer tissue was heat stable; that is, 65% activity was retained after incubation at 56°C for 60 min. The molecular weight of cathepsin L from gastric cancer tissue was estimated as 115 kD by gel filtration or 110 kD by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. The enzyme showed a different affinity for wheat germ agglutinin‐Sepharose than cathepsin L from gastric normal mucosa. These results suggest that cathepsin L from gastric cancer tissue may play an important role in gastric cancer invasion through the destruction of the surrounding extracellular matrix by its proteolytic activity.