Table 1. Endogenous polyamine transport activity of Drosophila S2 cells.

Cell suspensions were assayed for transport activity at both 1 and 5 min. The K_m (app) and V_max (app) values were determined by double-reciprocal plots (Lineweaver–Burk transformation) of transport activity in the presence of increasing concentrations of [¹⁴C]spermine or [¹⁴C]spermidine. Results are means±S.E.M. for three independent experiments performed in triplicate.

	Assay at 5 min		Assay at 1 min
Substrate	Km (app) (μM)	Vmax (app) (pmol/min per 106 cells)	Km (app) (μM)	Vmax (app) (pmol/min per 106 cells)
Spermine	3.67±0.54	23.47±1.43	–	–
Spermidine	5.80±1.41	21.43±2.52	5.91±0.73	18.76±1.14