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GrainGenes Reference Report: CRS-45-1868

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Reference	CRS-45-1868
Title	Characterization of Barley Tissue-Ubiquitous {beta}-Amylase2 and Effects of the Single Nucleotide Polymorphisms on the Enzyme's Thermostability
Journal	Crop Science
Year	2005
Volume	45
Pages	1868-1876
Author	Clark SE Hayes PM Henson CA
Abstract	There are two barley (Hordeum vulgare L.) {beta}-amylase genes encoding important starch-degrading enzymes. The endosperm-specific {beta}-amylase (Bmy1), the more abundant isozyme in cereal seeds, has been thoroughly characterized. The lesser abundant {beta}-amylase2 (Bmy2) has not been biochemically characterized from any cereal seeds. Characterization of Bmy2 from two commonly grown barley cultivars, Morex and Steptoe, was a major objective of this study. The bmy2 cDNAs were sequenced, expressed in Escherichia coli, and the recombinant enzymes (rBmy2) characterized. The relative hydrolysis rates of various {alpha}-D-glucans and the pH activity optima of Morex and Steptoe rBmy2s were the same and not significantly different from barley rBmy1. The Morex rBmy2 was 7{degrees}C more thermostable than the Steptoe rBmy2, determined by differences in their T50 values, and is more thermostable than any reported wild-type {beta}-amylase1. Three amino acid differences were identified between the two Bmy2 sequences and the contributions to enzyme thermostability evaluated by site-directed mutagenesis. Examination of mutant enzymes with one amino acid substitution revealed that each of the three residues contributed {approx}3{degrees}C to the thermostability of the Morex wild-type rBmy2. Mutant enzymes with two amino acid substitutions contributed {approx}5.6{degrees}C, and the triple amino acid mutant enzyme contributed {approx}8.7{degrees}C to thermostability. To date, no quantitative trait loci (QTL) for malting quality traits have been associated with the bmy2 locus. Should an association be discovered, the Morex bmy2 allele, containing D238, M337, and Q362, provides a discrete signature of a thermostable {beta}-amylase2 that could be targeted for marker assisted selection.
External Databases	http://crop.scijournals.org/cgi/content/abstract/45/5/1868

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