Abstract. Matrix vesicles, associated with initial calcification in cartilage, have been isolated from bovine fetal epiphyseal cartilage. Cartilage was digested with collagenase, then partitioned into seven fractions by differential centrifugation. The cellular fractions contained over 80% of the DNA in the digest. The extracellular fraction that contained matrix vesicles, in which apatite crystals were often seen on electron microscopy, also displayed the highest specific activity for alkaline phosphatase, pyrophosphatase, ATPase, and 5'-AMPase (EC 3.1.3

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Bovine nasal cartilage was studied by electron microscopy before and after extraction with 4 M guanidinium chloride or 1 .9 M CaC12 . These solvents removed matrix granules, basophilia, and 85% of the proteoglycan complex, measured as hexuronate . Simultaneously, many collagen fibrils were disaggregated into component microfibrils (approximately 40 A thick) . In contrast to the above solvents, exhaustive extraction with 0 .5 M guanidinium chloride removed 20% of the proteoglycan complex, and matrix granules were reduced in size but not in number . Extraction with 4 M CaC12 removed only 10% of the proteoglycan complex, did not remove matrix granules, and caused the normal banding pattern of collagen to disappear . The banding was restored by further treatment with trypsin . Trypsin, before or after 4 M CaC12 , removed matrix granules and 90% of the proteoglycan complex .We conclude that matrix granules are an electron microscopic representation of the proteoglycan complex, and consist of more than one proteoglycan macromolecule . It would appear that 4 M guanidinium chloride and 1 .9 M CaC12, in addition to removing most of the proteoglycan complex, also disaggregate some of the collagen fibrils into their component microfibrils.