Table 2. Characterization of native and Ile257 variant AfNiRs
AfNiR A458/595 A277/458 Mass (Da)a Specific activity (U/mg)b

Native 1.30 16.6 36847 (36843) 417 (44)c
I257V 1.33 18.5 15 (14) 521 (50)
I257L 1.26 19.1 1 (1) 108 (14)
I257M 1.35 17.0 22 (18) 17.9 (3.4)
I257A 1.32 17.9 43 (42) 15.6 (0.8)
I257G 1.36 17.0 57 (56) 10.4 (0.9)
I257T 1.29 17.1 12 (12) 5.90 (0.7)


a The absolute mass of the native is given along with the theoretical mass in parentheses. The values for the mutants are the absolute observed and theoretical mass (in parentheses) differences relative to the native.
b Specific activity values are reported as an average of at least three trials.
c Values in parentheses represent the standard error.