Poster: Enzymology

Abs # 230: Allelic variation in barley a-glucosidases

Presenter:	Muslin, Elizabeth H., emuslin@facstaff.wisc.edu
Authors	Muslin, Elizabeth H. (A)   Henson, Cynthia A (A)
Affiliations:	(A): Cereal Crops Research Unit, USDA-ARS

Starch degradation in barley (Hordeum vulgare) seeds results from the combined action of a-amylase, b-amylase, limit-dextrinase and a-glucosidase. The thermal stability of these enzymes is important because the conversion of barley starch to fermentable sugars during industrial ethanol production (e.g. brewing, fuel ethanol production) typically takes place at temperatures of 60-75°C. At these temperatures a-glucosidase has less than 5% of the activity it has at 30°C (Muslin et al., 2000). The thermolability of a-glucosidase could result in reduced efficiency of starch breakdown at these high temperatures. To increase the thermostability of a-glucosidase, we have created a thermostable a-glucosidase using site-directed mutagenesis (Muslin et al., 2002) which, when used in the industrial starch breakdown process (mashing), increased the amount of glucose produced by 29% (Muslin et al., 2003). We are now in the process of trying to find alleles in the Hordeum germplasm encoding a more thermostable enzyme. Differences in the thermostability of a-glucosidase were found in 7 cultivars of North American barley. These a-glucosidases were cloned and sequenced and single nucleotide polymorphisms (SNP) were found.