SUBSITE STRUCTURE OF SACCHAROMYCOPSIS ALPHA-AMYLASE SECRETED FROM SACCHAROMYCES-CEREVISIAE

The kinetic parameters (k(cat)/K(m)) and the cleaved-bond distributions for the hydrolysis of linear maltooligosaccharides G(n) (3 less-than-or-equal-to n less-than-or-equal-to 9) by Saccharomycopis alpha-amaylase (Sfamy) secreted from Saccharomyces cerevisiae were determined at pH 5.25 and 25-degrees-C. The subsite affinities of Sfamy were also evaluated from these data. The subsite structure of Sfamy is characteristic of the active site of an endo-cleavage type enzyme, consisting of internal repulsive sites with the catalytic residues and external attractive sites. Moreover, the pK(a) values of the catalytic residues were calculated from the pH dependence plot of the kinetic parameter (k(cat)/K(m)). The amino acid residues which contribute to the subsite affinities and the catalytic activity of Sfamy are proposed and compared with those of Taka-amylase A.