RESUMO
An abundant protein that is identical to the growth-associated protein pleiotrophin (PTN) has been isolated from dissociative extracts of bovine nasal and fetal epiphyseal cartilage. The yield from these tissues was at least 15 micrograms/g wet weight of cartilage. PTN was absent or was present only in trace amounts in mature articular cartilage. An analysis of tryptic fragments of PTN, held together with disulfide bonds, did not indicate any set pattern of cystine cross-links, which suggests a propensity for rapid refolding of the protein. PTN could not be isolated from thin (10 microns) slices of nasal cartilage in physiological extraction buffers, which indicates that it was tightly associated with the cell surface, was tightly associated with nonextractable matrix, or was an intracellular protein. Its appearance in various extraction media parallels that of histone H2b, a nucleosomal protein; this suggests a possible intracellular location for the protein. Immunohistochemical analysis of its distribution in fetal epiphysis indicated that it is associated with chondrocytes.
