REGULATION BY 1,4-DIAMINES OF THE ORNITHINE DECARBOXYLASE ACTIVITY INDUCED BY ORNITHINE IN PERIFUSED TUMOR-CELLS

Ornithine decarboxylase (ODC) activity of Ehrlich carcinoma cells was increased more than 36-fold after being maintained for 3.5 hr in vitro in a special chamber which allowed continuous perifusion with 0.5 mM ornithine; if incubated in vitro without perifusion the ODC activity was, of course, only 9-fold by the same concentration of ornithine. Ornithine withdrawal from the perifusion medium resulted in a decay of enzyme activity observed after 90 min; this decay was prevented by addition of 55-mu-M pyridoxal to the medium. The 1,4-diamines putrescine, spermidine, spermine, agmatine, histamine, serotonin, tryptamine, chlorpheniramine and harmaline at 55-mu-M strongly suppressed ODC induction by 0.5 mM ornithine in perifused Ehrlich ascites cells. Methyl derivatives also behave as strong inhibitors of ODC induction. On the contrary, N-acetylation paralleled with a decrease in the inhibition capacity: 55-mu-M N-acetyl putrescine, N-acetyl serotonin or N-omega-acetylhistamine suppressed ODC induction by ornithine in 66, 64 and 19%, respectively. The addition to the perifusion medium of the same concentrations of 1,3-diamines (1,3-diaminopropane, 1,3-diamino-2-propanol or the alkaloid gramine) as well as 1,5-diamines (1,5-diaminopentane and the antihistaminic doxylamine or cimetidine) failed to suppress the induction of ODC activity by ornithine. Interestingly, 1,4-benzenediamine, which strongly inhibits ODC activity when the induced enzyme is assayed in its presence, did not suppress the induction of the enzyme when both 0.5 mM ornithine and 55-mu-M 1,4-benzenediamine were present in the perifusion medium. The inhibitory capacity in down-regulating ODC is not due to differences in the diamine uptake by the cells. The results suggest that the N-N distance (6 angstrom) and the charge of one amino group are important chemical characteristics for regulatory effects.