Patent ID: 6969783

Claim:
A polynucleotide encoding a mutant large subunit of a maize endosperm ADP-glucose pyrophosphorylase polypeptide, or a biologically-active fragment of said mutant polypeptide, wherein said mutant polypeptide comprises amino acid mutations at two or more sites in the amino acid sequence of said polypeptide and wherein when said mutant polypeptide is expressed with a small subunit of ADP-glucose pyrophosphorylase to form a mutant ADP-glucose pyrophosphorylase enzyme, said mutant enzyme, or a biologically-active fragment of said mutant enzyme, exhibits increased heat stability relative to wild typo maize endosperm ADP-glucose pyrophosphorylase enzyme, wherein said mutant polypeptide encoded by said polynucleotide comprises a first amino acid mutation wherein the histidine amino acid in said maize polypeptide at position 333 in the amino acid sequence or the wild type large subunit of ADP-glucose pyrophosphorylase polypeptide of maize is replaced by an amino acid that confers said increased heat stability on said mutant enzyme, and wherein said mutant polypeptide encoded by said polynucleotide comprises a second amino acid mutation wherein the alanine amino acid in said maize polypeptide at position 177 in the amino acid sequence of the wild type large subunit of ADP-glucose pyrophosphorylase polypeptide of maize is replaced by an amino acid that confers said increased heat stability on said mutant enzyme.