Important for the overall degradation of proteins in lysosomes. Essential for adult male and female fertility. May play a role in digestion. Specificity close to that of papain. As compared to cathepsin B, cathepsin L exhibits higher activity toward protein substrates, but has little activity on Z-Arg-Arg-NHMec, and no peptidyl-dipeptidase activity. Dimer of a heavy and a light chain linked by disulfide bonds. In the embryo, predominantly expressed in the midgut. Also expressed in larval alimentary organs such as salivary gland and midgut including gastric caeca. Expressed in embryo, larva, pupa and adult. Flies exhibit wing and pigmentation defects. Females are sterile, males are partially sterile. Belongs to the peptidase C1 family. Intron retention.