MUTATIONS TO ALTER ASPERGILLUS-AWAMORI GLUCOAMYLASE SELECTIVITY - II - MUTATION OF RESIDUE-119 AND RESIDUE-121

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.