Table 4.
Effect of spermidine concentration in the growth medium on the level of ornithine decarboxylase in Δspe1Δspe2 cells containing the pVT101U/pSPE1 plasmid (Y465) and on the degradation of ornithine decarboxylase after cycloheximide treatment
| Spermidine concentration in medium | 5 × 10−4 M | 5 × 10−5 M | 5 × 10−6 M | 5 × 10−7 M | 5 × 10−8 M | 1 × 10−8 M |
|---|---|---|---|---|---|---|
| Doubling time, hr* | 1.7 | 1.8 | 1.8 | 2.1 | 2.7 | 3.2 |
| ODC activity† before cycloheximide | 830 | 560 | 780 | 2,300 | 2,050 | 1,710 |
| ODC activity 90 min after cycloheximide‡ | 290 (35%) | 270 (48%) | 280 (36%) | 1,590 (69%) | 2,110 (103%) | 1,570 (92%) |
*
Determined in a parallel run in the absence of cycloheximide. The doubling time in 1 × 10−9 M spermidine was 4.4 hr. Without any added spermidine, the doubling time of the deprived cells was >20 hr.
†
nmol CO2 formed/hr/mg protein.
‡
Final concentration, 200 μg/ml.