The 210th lysine (K210) at the active site in Saccharomycopsis fibuligera α-amylase was altered to arginine (R) or asparagine (N) by site-directed mutagenesis. Replacement of K210 by R strengthened the 7th and weakened the 8th subsite affinities. K210 was found to contribute to both the 8th and the 7th subsites. The catalytic activity of the K210R enzyme for the hydrolysis of maltose (G2) was three-times higher than that of the native enzyme due to an increase in the affinity of the 7th subsite adjacent to the catalytic site, whereas the activity of the K210N enzyme for G2 was decreased to 1% of that of the native enzyme by a reduction in the 7th subsite affinity.
