Branching enzyme catalysis, functional amino acid residues

Amino Acid Residues that are Functional in Branching Enzyme Catalysis... 

As indicated in Table 4.12, four regions which constitute the catalytic regions of amylolytic enzymes are conserved in the starch-branching isoenzymes of maize endosperm, rice seed and potato tuber, and the glycogen-branching enzymes of E. coli.286,281 It would be of interest to know whether the seven highly conserved amino acid residues of the a-amylase family listed in bold letters in Table 4.12 are also functional in branching enzyme catalysis. Further experiments, such as chemical modification and analysis of the three-dimensional structure of the BEs, would be needed to determine the nature of its catalytic residues and mechanism. 

Indeed, the seven highly conserved amino acid residues of the a-amylase family also appear to be functional in branching enzyme catalysis. A series of experiments,288 in which amino acids were replaced by site-directed mutagenesis, suggest that the conserved Asp residues of regions two and four and the Glu residue of region 3 (Table 4.12, in bold letters) are important for BEII catalysis. Their exact functions,... 

Some of the eight highly conserved amino-acid residues of the a-amylase family may also be functional in branching enzyme catalysis. Research using... 

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