Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 7/21/2001
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Differences in total beta-amylase activity exist between enzymes from a malt quality (MQ) and a feed quality (FQ) barley (Hordeum vulgare) cultivar. Others have documented differences in the structure of the genomic DNA encoding endosperm specific beta-amylase 1 (Bamy1) and attributed the differences in enzymatic activity to these genomic differences. The Bamy1 deduced amino acid sequences from the malt quality and the feed quality cultivars studied differ at only two positions. To determine the impact on the enzyme's biochemical characteristics imparted by these single nucleotide polymorphisms, site directed mutagenesis was used to change these two residues. The wildtype and mutant proteins were expressed in E. coli and purified. The recombinant wildtypes did not show differences in activity per mg of Bamy1 protein. However, their thermostabilities were different. The MQ recombinant beta-amylase retained 46 to 55% of its activity at 57C while the FQ recombinant beta- amylase retained 3 to 34.5% of its activity at the same temperature. One mutant enzyme behaved similarly to the FQ recombinant beta-amylase in that it retained only 4.5 to 17% of its activity at 57C. The second mutant enzyme retained 25 to 44% of its activity at 57C, which is approximately half of the activity of the MQ beta-amylase.