Evidence for the importance of puromycyl peptides in the inhibition by puromycin of cell aggregation in vitro.

Trypsin-dissociated cells from the muscle tissue of 9-day-old chick embryos were employed to investigate the effects of cycloheximide and a puromycin-cycloheximide mixture on cell aggregation, protein synthesis and respiratory metabolism. Cycloheximide when introduced at a concentration of 10 /Jg/ml into a suspension of cells in Eagle's MEM inhibited aggregation by 25 % at 24 h. At this time an inhibition of 40 % was apparent in the presence of a mixture of cycloheximide and puromycin both at a concentration of 10 /ig/ml. Both cycloheximide and the cycloheximide-puromycin mixture arrested protein synthesis of rotated cells by 90 % within 15 min of introducing the antibiotics into cell suspensions. The antibiotics retained their inhibitory effects on protein synthesis for the 24-h period of rotation. Cycloheximide inhibited cellular oxygen uptake and carbon dioxide evolution of rotated cells by 25 % at the end of the 24-h experimental period. At this time an inhibition of 30 % was observed in the presence of the cycloheximide-puromycin mixture. The release of radioactive carbon dioxide by cycloheximide-treated cells was inhibited by 46 % at 24 h. In the presence of the antibiotic mixture, "COj release was inhibited by 30 % at 4 h, but after 8 h very little further COj was evolved. As a control, puromycin (10/tg/ml) inhibited cell aggregation and respiration to an extent similar to that previously reported. The results are discussed in terms of puromycyl peptides producing a metabolic effect on cell aggregation. It is considered that this is additional to the effect of puromycin inhibiting aggregation through the arrest of protein synthesis.