. 2021 Mar 16;12:643508. doi: 10.3389/fmicb.2021.643508

TABLE 2.

Effects of metal ions and inhibitors on activity of the protease of strain 1A02591.

Metal ion (2 mM)	Relative activity^a (%)	Metal ion (2 mM)	Relative activity^a (%)	Inhibitors^b (2 mM)	Residual activity^c (%)
Control	100.00	Mn²⁺	120.22 ± 7.59	Control	100.00
Ca²⁺	99.11 ± 5.18	Ba²⁺	98.55 ± 0.17	PMSF	54.54 ± 2.55
Li⁺	104.86 ± 7.21	Fe²⁺	76.79 ± 3.41	EDTA	51.42 ± 3.59
K⁺	97.80 ± 2.05	Zn²⁺	83.20 ± 3.52	EGTA	ND
Mg²⁺	96.02 ± 1.90	Sr²⁺	102.17 ± 1.70	o-P	31.99 ± 2.67
Cu²⁺	72.32 ± 6.46	Co²⁺	85.87 ± 4.31
Ni²⁺	57.14 ± 3.21	Sn²⁺	101.87 ± 1.79

^a The protease activity was measured at 70°C and pH 7.5 with casein as the substrate. The activity (298.25 ± 18.33 U/mL) of the protease without any metal ion was used as a control (100%). ^b PMSF, phenylmethylsulfonyl fluoride; EDTA, ethylene diamine tetraacetic acid; EGTA, ethylene glycol tetraacetic acid; o-P, o-phenanthroline. ^c The residual activity of the protease was measured at 70°C and pH 7.5 with casein as the substrate after the protease was incubated with an inhibitor at 4°C for 60 min. The activity (298.25 ± 18.33 U/mL) of the protease without any inhibitor was used as the control (100%). The data represent the mean ± SD of three experimental repeats. ND means that the enzyme activity was not detectable.