To examine the potential participation of the plasma membrane in differentiation, we studied the enzymatic activities of 5'-nucleotidase and adenylate cyclase as a function of chondrocyte maturation. 16-day-old chick embryo tibiae epiphyses were dissected into proliferative, growing and hypertrophying zones. Partially purified membrane fractions prepared by differential centrifugation from the respective tissue segments were assayed for enzymatic activity. Cell suspensions from the same segments were examined cytochemically for the presence of 5'-nucleotidase. The findings show that the 5'-nucleotidase activity of the chick embryo epiphyseal cartilage has the following characteristics: (a) it has a Km of about 25 muM for 5'AMP, and is inhibited by a mixture of 2' and 3'AMP (apparent Ki about 10(-4) M) and by AOPCP; (b) it is predominantly localized at the cell surface but is also detected in the cytoplasm and in association with nuclear heterochromatin; and (c) it increases 10-fold (on a DNA basis) during the maturation of the epiphyseal cartilage cells. The adenylate cyclase activity has these characteristics: (a) it does not change during chondrocyte maturation (on a DNA basis); (b) its susceptibility to adenosine inhibition decreases at least 10-fold. The implication of these findings relative to a possible role of adenosine in cellular communication is discussed.

This content is only available as a PDF.