Soares-da-Silva P, Serrão M P, Vieira-Coelho M A
Institute of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal.
Cell Biol Int. 1996 Aug;20(8):539-44. doi: 10.1006/cbir.1996.0070.
The Vmax values (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-PK1 cells (4.37 +/- 0.08). However, in both cell lines decarboxylation reaction was a saturable process with similar K(m) values (OK cells = 1.1 mM (0.3, 1.8); LLC-PK1 cells = 1.8 mM (1.6, 2.1)). Contrariwise to OK cells, decarboxylation of L-DOPA to dopamine in LLC-PK1 cells 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 of L-DOPA (10 to 500 microM) followed a non-linear kinetics in both cell lines; the process of L-DOPA decarboxylation was saturated at low concentrations of L-DOPA with an apparent K(m) value of 11 microM (0.2, 22.6) in OK cells and 27.4 microM (11.1, 43.7) in LLC-PK1 cells. The formation of dopamine in LLC-PK1 cells (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-PK1 cells appear to be endowed with a greater ability to form dopamine from exogenous L-DOPA when compared to OK cells.
OK细胞中AAAD的Vmax值（以nmol/mg蛋白质/15分钟计）为(0.94±0.08)，发现其显著低于LLC-PK1细胞中的值(4.37±0.08)(P<0.01)。然而，在两种细胞系中，脱羧反应都是一个具有相似K(m)值的可饱和过程（OK细胞=1.1 mM(0.3,1.8)；LLC-PK1细胞=1.8 mM(1.6,2.1)）。与OK细胞相反，LLC-PK1细胞中L-DOPA脱羧生成多巴胺的过程在孵育120分钟之前遵循线性（7.6±0.1 pmol/mg蛋白质/分钟）非饱和动力学。在两种细胞系中，多巴胺的生成随L-DOPA浓度升高（10至500μM）遵循非线性动力学；L-DOPA脱羧过程在低浓度L-DOPA时达到饱和，OK细胞中表观K(m)值为11μM(0.2,22.6)，LLC-PK1细胞中为27.4μM(11.1,43.7)。LLC-PK1细胞中多巴胺的生成量（Vmax=2097±113 pmol/mg蛋白质/6分钟）是OK细胞中生成量（Vmax=153±10 pmol/mg蛋白质/6分钟）的13.7倍。总之，与OK细胞相比，LLC-PK1细胞似乎具有更强的从外源性L-DOPA生成多巴胺的能力。
