The lack of altered enzyme molecules in "senescent" mouse embryo fibroblasts in culture

In order to compare the biochemical events occurring in senescent animals in vivo with those of fibroblasts demonstrating a limited life span in tissue culture, experiments were performed to determine whether altered enzyme molecules are produced in late passage mouse embryo fibroblasts in tissue culture. Such altered enzymes have been previously described by us in both senescent mice and nematodes. Fibroblast cultures, initiated from BALB/c embryos underwent approximately 7 population doublings before reaching stationary phase. A comparison was made of the enzyme activity and the quantity of antigen of the enzyme aldolase present in these cultures. The amound of aldolase per cell as well as the amount of enzyme per unit of antigen remained constant throughout the in vitro lifespan of these cells. Further evidence testifying to a lack of enzyme alteration in vitro was obtained in experiments testing temperature sensitivity. The aldolase from all passages was equally sensitive to heating at 60 degrees C.