THE ACTION OF GERMINATED BARLEY ALPHA-AMYLASES ON LINEAR MALTODEXTRINS

The actions of barley alpha-amylase isozymes 1 and 2 (EC 3.2.1.1) on malto-oligosaccharides and their p-nitrophenyl glycosides were similar, but not identical. For each isozyme, transglycosylation occurred with small substrates that were hydrolysed with difficulty, whereas the rates of hydrolysis increased with increase in the size of the substrate for both the malto-oligosaccharides and the p-nitrophenyl glycosides. A p-nitrophenyl group was found to mimic a glucose residue to a large extent. The differences in action of the isozymes are believed to be caused by differences at more than one subsite of the active site. A lysine-arginine substitution is postulated to account for some of the observed variations.