Effects of single nucleotide polymorphisms in β-amylase1 alleles from barley on functional properties of the enzymes

Differences in extractable β-amylase (1,4-α-D-glucan maltohydrolase, EC 3.2.1.2) activities exist between enzymes from malt and feed barleys (Hordeum vulgare L.). Others have documented few differences in the β-amylase (bmy1) gene coding regions and large differences in the non-coding regions of genomic DNA for endosperm specific β-amylases from malt and feed barleys. Researchers correlated differences in intron III with different activity levels in the seeds. Here we demonstrate that differences in the coding regions of bmy1 from a malt (‘Morex’) and a feed (‘Steptoe’) barley significantly affected the biochemical properties of the enzymes. We evaluated the contributions of the three single nucleotide polymorphisms that caused differences in the amino acid sequences at positions 115, 165, and 430. Two polymorphisms (positions 115 and 430) were found to impact the enzymatic activity of β-amylase. The effect of the single nucleotide polymorphism at position 165 was dependent upon the identity of the amino acid in position 115. The contributions of the three single nucleotide polymorphisms to β-amylase thermostability varied with assay temperature. These biochemical results explain the contribution of the favorable bmy1 allele from the feed barley Steptoe to the quantitative trait loci found on chromosome 4H at the bmy1 locus.