Pepstatin inhibits the digestion of hemoglobin and protein-polysaccharide complex by cathepsin D

Pepstatin, a peptide inhibitor of pepsin isolated from cultures of Actinomycetes, is shown to be a powerful inhibitor of cathepsin D preparations obtained from bovine uterus and rabbit ear cartilage. The digestion of hemoglobin at pH 3.2 is completely blocked by pepstatin at a 1:1 molar ratio of inhibitor to enzyme. The digestion at pH 5 of protein-polysaccharide-light complex from bovine nasal cartilage is 98% inhibited.