Models for the action of barley alpha-amylase isozymes on linear substrates.
The formation of maltodextrins, G1 to G12, during the hydrolysis of amylose by alpha-amylases 1 and 2 from barley malt was followed by HPLC. Similar, but not identical, distributions of products were obtained with the two alpha-amylase components. Maltose, G6, and G7 were major products, but G7 was degraded as hydrolysis proceeded. alpha-Amylase 1 produced more G1 and G3 than did alpha-amylase 2 at all stages of hydrolysis. Products formed during the hydrolysis of G9, G10, G11, and G12 by the two alpha-amylases were also determined. A different spectrum of products was observed with each substrate and small differences were observed in the action pattern of the two alpha-amylases, e.g., G3 and G7 were the major products formed during the hydrolysis of G10 by alpha-amylase 1, whereas G2 and G8 were the major products formed by alpha-amylase 2 on the same substrate. These results were used to develop a model of the active site of barley malt alpha-amylases. This site contains ten contiguous subsites with the catalytic site situated between subsites 7 and 8. The model can be used to predict hydrolysis patterns of amylose and maltodextrins by cereal alpha-amylases.
Grain Research Laboratory, Canadian Grain Commission, Winnipeg, Manitoba.
E A
EA
MacGregor
A W
AW
MacGregor
L J
LJ
Macri
J E
JE
Morgan
D002240:Carbohydrate Sequence; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D005936:Glucans / Q000378:metabolism; D001467:Hordeum / Q000201:enzymology*; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D008962:Models, Theoretical; D008969:Molecular Sequence Data; D011134:Polysaccharides / Q000032:analysis / Q000378:metabolism*; D013379:Substrate Specificity; D000516:alpha-Amylases / Q000378:metabolism*
D005936:Glucans; D007527:Isoenzymes; D011134:Polysaccharides; C008315:maltodextrin; D000516:alpha-Amylases