Variation in α-amylase and α-amylase inhibitor activities in barley malts

Malts of barley genotypes exhibiting a wide range of α-amylase activities were used to determine if these differences resulted from the absence of functional products of one of the two gene families which encode barley α-amylase. Additional studies were conducted to determine if α-amylase activities reflect differences in activities of a specific proteinaceous α-amylase inhibitor. These malts had a 43-fold variation in in vitro α-amylase activities. When examined by isoelectric focusing and activity staining, all genotypes exhibited the same α-amylase isozyme patterns. In vitro amylase inhibitor activities varied only three-fold. The correlation coefficient between inhibitor and α-amylase activities was -0·92 (P ⩽ 0·01). Examination of two of these malts by isoelectric focusing followed by inhibitor activity staining, showed that both malts had six bands of activity with one very prominent band. We conclude (1) that no gross absence of functional α-amylase isozymes occurs, thus both gene families coding for α-amylases are expressed, and (2) that levels of α-amylase inhibitor may be an important factor, but probably not the only factor, in regulating malt α-amylase activities.