Enhancement of thermal killing by polyamines. IV. Effects of heat and spermine on protein synthesis and ornithine decarboxylase activity.

Protein synthesis is shown to be very heat-sensitive in Chinese hamster cells. It is shut off completely following 15-20 min at 42 degrees C whereas RNA and DNA syntheses are affected only after much longer exposure times. Cells recover from inhibition of protein synthesis upon transfer to 37 degrees C. The degree of recovery is inversely related to the duration of heat exposure and it fits cell survival quantitatively. Cells which become temporarily heat-resistant by prior heat-treatment, are able to recover translational capacity even after a very long exposure to heat (4 h at 42 degrees C). Spermine, which enhances heat-induced cell killing, does not increase the response to heat of protein, RNA and DNA synthesis. Ornithine decarboxylase (ODC, EC 4.1.1.17) activity is lost exponentially following a 20 min lag period during exposure at 42 degrees C. The half-life observed (12 min) is in agreement with the reported values of half-life of decay of ODC in other systems. It is concluded that the loss of activity is due to the shut-off of translation. The activity of ODC is recovered upon transfer to 37 degrees C. The presence of spermine during heating does not affect the loss of enzyme activity but delays its recovery by about 3 h upon transfer to 37 degrees C.