Membrane changes during cartilage maturation. Increase in 5'-nucleotidase and decrease in adenosine inhibition of adenylate cyclase.

Open Access
Publisher Website
Google Scholar
Abstract
To examine the potential participation of the plasma membrane in differentiation, the enzymatic activities of 5''-nucleotidase and adenylate cyclase were studied as a function of chondrocyte maturation. Chick embro tibiae epiphyses (16 day old) 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 5''-nucleotidase activity of the chick embryo epiphyseal cartilage had the following characteristics: it had a Km of about 25 .mu.M for 5''-AMP, and was inhibited by a mixture of 2''- and 3''-AMP (apparent Ki about 10-4 M) and by AOPCP [adenosine-5''-methylenediphosphonate]; it was predominantly localized at the cell surface but was also detected in the cytoplasm and in association with nuclear heterochromatin; and it increased 10-fold (on a DNA basis) during the maturation of the epiphyseal cartilage cells. The adenylate cyclase activity had these characteristics: it did not change during chondrocyte maturation (on a DNA basis); and its susceptibility to adenosine inhibition decreased at least 10-fold. The possible role of adenosine in cellular communication is discussed.