Isolation and characterization of cathepsin D from human gastric mucosa

Abstract

The molecular weight of the enzyme, purified by ion-exchange chromatography and affinity chromatography, was determined by gel filtration on Sephadex G-100 as 49 000. After treatment with 2-mercaptoethanol, polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate resolved the enzyme into two chains, of molecular weights 33 000 and 18 000. This shows that in the native state the enzyme is composed of one light and one heavy chain. Isoelectric focusing in polyacrylamide gel gave four bands, the isoelectric points being 5.5, 6.1, 6.5 and 7.1. The optimum protein substrate (pH optimum 3.2-3.6) was haemoglobin. The best synthetic substrate was methyl ester of pyroglutamyl-histidyl-phenylalanyl-phenylalanyl-alanyl-leucine. The protease was inhibited by the inhibitor of cathepsin D from the potato tubers. It is concluded that the enzyme is cathepsin D from gastric mucosa.