Table 2.

Effect of metal ions on EST4 activity

Ion	Relative activity (%)a
	1 mM	5 mM
Control	100.0 ± 4.2	100.0 ± 0.8
EDTA	97.0 ± 3.6	95.2 ± 2.1
Mg2+	95.1 ± 2.9	92.2 ± 0.8
Ca2+	94.1 ± 2.9	98.0 ± 1.0
Mn2+	92.4 ± 4.7	83.8 ± 3.6
Fe2+	87.6 ± 3.3	57.4 ± 1.0
Cu2+	87.1 ± 5.3	66.9 ± 4.8
Ni2+	78.8 ± 2.5	67.1 ± 2.4
Fe3+	77.0 ± 3.0	57.1 ± 4.8
Co2+	74.5 ± 4.0	44.5 ± 5.8
Zn2+	63.6 ± 3.0	31.6 ± 3.5

^aThe activity toward p-nitrophenyl butyrate without any metal ions was taken as 100 %. All measurements were repeated three times