RESUMEN
1. Two proteoglycans, PG1 and PG2, have been isolated from shark cartilage. Both are highly polydisperse and large (molecular mass: 1-10 x 10**6 Daltons) and contain chondroitin sulfate and keratan sulfate side chains, but PG2 is somewhat smaller tham PG1 and contains less keratan sulfate. 2. Monoclonal antibodies were raised against PG1. Many antibodies were obtained and one of them, MST1, was subcloned and furter characterized. This monoclonal antibody reacts with PG1 and PG2 from shark cartilage and also with aggrecan from bovine trachea cartilage. Chondroitinase AC-treated proteglycans react MST1, indicating that the antibody does not reconize chondroitin sulfate. MST1 also recognizes aggrecan from human cartilage and a proteoglycan from bovine brain (neurocan) but it does reconize proteoglycans from rat Walker tumor, fetal calf muscle and decorin from human myoma. 3. Using MST1 we were able to demonstrate that both PG1 aggregate with hyaluronic acid