Control of ornithine decarboxylase activity by polyamines and absence of antizyme in Tetrahymena

Involvement of antizyme-like regulatory protein in polyamine-caused repression of ornithine decarboxylase in insect-derived Trichoplusia ni 5 cells

Addition of spermidine to culture medium of insect cells, Trichoplusia ni 5, at a low cellular density suppressed ornithine decarboxylase (ODC; EC 4.1.1.17) activity and induced ODC inhibitory activity. The inhibitory factor was non-dialyzable, temperature-sensitive, and could reversibly form an inactive complex with ODC. It showed a time-independent and non-stoichiometric pattern of inhibition. Upon addition of spermidine to cultured cells with preinduced ODC, the enzyme decayed more rapidly than after addition of cycloheximide. These data strongly suggested that ODC of Tn5 cells is under negative feedback control by polyamines, in which an antizyme-like regulatory protein plays an essential role.