Table 4.

Effect of inhibitors on TNAP enzyme activity. When cysteine and mercaptopyruvate (MPA) were combined, each inhibitor at concentration shown, except MPA alone (0, 20, 200, 2000 μM). At least 4 sets of experiments in duplicates were performed. Values are mean ± standard deviation.

EnzymeSubstrateInhibitor Concentration, μMCysteine (%)Inhibitors MPA Nmol Pi/Unit ALP/Min (%)Cysteine + MPA (%)
TNAP (Piase)pNPP 2000 μM029 ± 1.9 (100)32 ± 10 (100)28 ± 1.7 (100)
4028 ± 2.8 (98)26 ± 8 (81)8 ± 1.6* (29)
40011 ± 1.3* (37)17 ± 1.0* (53)4 ± 0.8* (14)
40004 ± 1.0* (12)10 ± 2.0* (31)3 ± 0.2* (12)
TNAP (PPiase)Pyrophosphate 2000 μM027 ± 1.9 (100)56 ± 3.0 (100)55 ± 16.4 (100)
4030 ± 2.0 (110)53 ± 3.0 (93)21 ± 4.5* (39)
40018 ± 1.3* (66)39 ± 5.0* (70)19 ± 4.7* (34)
40002 ± 1.1* (6)27 ± 5.0* (54)14 ± 3.7* (25)
TNAP (CPPD crystal dissolution)CPPD 345 μM (100 μg)00.46 ± 0.07 (100)0.26 ± 0.11 (100)0.26 ± 0.02 (100)
400.49 ± 0.09 (107)0.25 ± 0.01 (96)0.23 ± 0.01 (88)
4000.43 ± 0.04 (93)0.24 ± 0.01 (92)0.10 ± 0.007* (38)
40000.15 ± 0.02* (33)0.07 ± 0.01* (27)0.00 ± 0.05* (0)
  • * Calculated value with inhibitor present is statistically significantly different (p < 0.05) from the value with no inhibitor. TNAP: tissue-nonspecific alkaline phosphatase; CPPD: calcium pyrophosphate dihydrate; pNPP: p-nitrophenyl phosphate; ALP: alkaline phosphatase.