TheVmaxvalues (in nmol/mg protein/15 min) for AAAD in OK cells (0.94±0.08) were found to be significantly (P<0.01) lower than those observed in LLC-PK1cells (4.37±0.08). However, in both cell lines decarboxylation reaction was a saturable process with similarKmvalues (OK cells=1.1 mm(0.3, 1.8); LLC-PK1cells=1.8 mm(1.6, 2.1)). Contrariwise to OK cells, decarboxylation ofl-DOPA to dopamine in LLC-PK1cells followed a linear (7.6±0.1 pmol/mg protein/min) non-saturable kinetics till 120 min of incubation. The formation of dopamine from increasing concentrations ofl-DOPA (10 to 500 μm) followed a non-linear kinetics in both cell lines; the process ofl-DOPA decarboxylation was saturated at low concentrations ofl-DOPA with an apparentKmvalue of 11 μm(0.2, 22.6) in OK cells and 27.4 μm(11.1, 43.7) in LLC-PK1cells. The formation of dopamine in LLC-PK1cells (Vmax=2097±113 pmol/mg protein/6 min) was 13.7-fold that occurred in OK cells (Vmax=153±10 pmol/mg protein/6 min). In conclusion, LLC-PK1cells appear to be endowed with a greater ability to form dopamine from exogenousl-DOPA when compared to OK cells.