Influence of pH on the hydrolysis of p-nitrophenyl maltodextrins by alpha-amylase 2 from malted barley

The action of barley malt alpha-amylase 2 (E.C. 3.2.1.1) on p-nitrophenyl derivatives of maltodextrins was studied at pH 4.8, 6.0 and 7.8. Distributions of products from any one substrate changed little with pH, but a difference in behaviour was observed at pH 4.8 between longer and shorter substrates. With long substrates, such as p-nitrophenyl alpha-malto-octaoside, the enzyme showed high activity at pH 4.8 and 6.0, while for shorter substrates, enzyme activity was much less at pH 4.8 than at 6.0.