α-Amylase Isozymes in Gibberellic Acid-treated Barley Half-seeds

The presence of multiple forms of alpha-amylase in gibberellic acid-treated embryoless barley half-seeds was demonstrated by separation on diethylaminoethyl-Sephadex and isoelectric focusing polyacrylamide gel disc electrophoresis. Two major alpha-amylase fractions (A and B), each consisting of two to three isozyme components, were purified. alpha-Amylase fractions A and B were distinguishable in their reaction patterns. The optimal pH of fraction A alpha-amylase was found to reside in the acidic side (pH 5.0), as was determined by analyzing the reducing sugars formed as well as the paper chromatographic detection of reaction products. At neutral pH, 6.9, fraction A exhibited weak amylolytic activity in forming maltose. The alpha-amylase activity in fraction A was markedly stimulated by heat treatment (70 C/15 minutes). Fraction B, constituting a major part of amylases in the endosperm extract, was also found to be composed of alpha-amylase, as evidenced by the loss of enzyme activity upon allowing fractions A and B to stand at pH 3.3 for a prolonged period. The possible physiological function of the two different types of alpha-amylase in the carbohydrate breakdown of barley seeds is discussed.