Ty. Fang et al., MUTATIONS TO ALTER ASPERGILLUS-AWAMORI GLUCOAMYLASE SELECTIVITY - II - MUTATION OF RESIDUE-119 AND RESIDUE-121, Protein engineering, 11(2), 1998, pp. 127-133
Mutations Ser119-->Glu, Ser119-->Gly, Ser119-->Trp, Gly121-->Ala and G
ly121-->Ala/Ser411-->Gly were constructed in glucoamylase to change su
bstrate specificity. Mutation Ser411-->Gly was already known to decrea
se glucoamylase selectivity toward isomaltose formation and to increas
e peak glucose yield. All mutated glucoamylases had slightly lower spe
cific activities on maltose than on wild-type glucoamylase, Ser119-->G
lu, Ser119-->Gly and Ser119-->Trp glucoamylases were about as active o
n isomaltose and DP 4-7 maltooligosaccharides as wild-type glucoamylas
e. Gly121-->Ala and Gly121-->Ala/Ser411-->Gly glucoamylases were less
active. At 55 degrees C Ser119-->Glu, wild-type, Ser119-->Trp, Ser119-
->Gly, Gly121-->Ala and Gly121-->Ala/Ser411-->Gly glucoamylases had pr
ogressively higher peak glucose yields, generally in the opposite orde
r to their activities. There was also an inverse correlation between p
eak glucose yield and ratio of initial rate of isomaltose production f
rom glucose condensation to that of glucose production from maltodextr
in hydrolysis. The effect of mutations Gly121-->Ala and Ser411-->Gly w
as not additive in predicting the effect of the double mutation on the
ratio or on peak glucose yield.