Table 3.

Kinetic parameters V_max and K_M of TNAP pyrophosphatase and pyrophosphatase assay: effect of mercaptopyruvate (MPA) and cysteine combined. At least 4 sets of experiments in duplicates were performed. Values are mean ± standard deviation.

MPA, μM Cysteine, μM	Phosphatase [Ca⁺⁺] = [Mg⁺⁺] = 1 mM		Pyrophosphatase [Ca⁺⁺] = [Mg⁺⁺] = 1 mM
MPA, μM Cysteine, μM	V_max	K_M	V_max	K_M
0	27 ± 1.7	27 ± 1.6	48 ± 1.4	89 ± 17
40	7.5 ± 1.8^*	5.7 ± 1.9^*	18 ± 5.1^*	71 ± 18
400	3.3 ± 0.9^*	5.2 ± 0.7^*	16 ± 6.9^*	139 ± 118
4000	2.6 ± 0.4^*	15 ± 2.9^*	11 ± 3.7^*	85 ± 88

↵* Calculated value with MPA present is statistically significantly different (p < 0.05) from the value with no MPA.