The synthesis, turnover, and artificial restoration of a major cell surface glycoprotein

A large glycoprotein (molecular weight equals 220,000 daltons) can be isolated from the surfaces of chick embryo fibroblasts. Such a protein had been shown by others to be present on normal cells in vitro, but missing from transformed variants of these cells, suggesting a possible role in growth control. We have estimated the turnover rate of this cell surface protein (CSP) and show that it is not more rapid than that of other cell proteins. We have also examined the resynthesis of CSP after removal from cells by trypsinization. This restoration is gradual, requiring more than 24 hr, and is affected by cell density. Restoration can be blocked by cycloheximide. Using cycloheximide to maintain cells depleted of CSP, we have demonstrated that isolated CSP can be progressively reabsorbed at 37 degrees C onto these denuded cell surfaces, and that this adsorption is not observed at 4 degrees C. This information on the turnover, depletion, and restoration of CSP may provide a means of directly testing its function.