UNACTIVATED papain, injected intravenously into rabbits, passes from the blood to cartilage tissues where it is activated locally, causing ear collapse due to depolymerization of chondromucoprotein (chondroitin sulphateâ protein complexes). The enzymatic products (for which the term â chondromucopeptidesâ is proposed) leach out of the cartilage into the blood and are excreted in the urine¹.