P. yoelli nigeriensis has an acid endoprotease (cathepsin D) and an endoarylamidase. 2. The acid endoprotease is specific towards haemogloblin. It is found in 2 molecular forms, of molecular weight 100,000 and 50,000. It is inhibited by hematin and pepsatin. 3. In mouse normal red blood cells we find an acid protease having physico-chemical properties similar to those of the enzyme present in P. yoelii nigeriensis extracts, except as regards the pHi. 4. In parasite extracts there exists an enzyme active on the synthesis substrate N-acetyl alanine 4 nitro anilide. The main properties of this enzyme have been determined. 5. This enzyme must be also involved in the mechanism of haemoglobin degradation.
