Multiple components of alpha-amylase in germinating tubers of a yam, Dioscorea dumetorum.

alpha-Amylase from germinating tubers of a yam Dioscorea dumetorum was extracted and purified by four steps of purification. A total yield of 23.1% was obtained with over 1,600-fold increase in specific activity. Three distinct amylolytically active protein forms were resolved upon treatment of the preparation on DEAE-cellulose ion exchange chromatography at pH 8.3. All the partially purified alpha-amylase fractions have similar physical properties with respect to pH optimum, Km values, molecular weights, and energies of activation. Qualitative paper chromatographic analysis of the alpha-amylase-amylose digest revealed variable product specificity for the three alpha-amylase fractions. One form exhibited a dual product specificity for the formation of maltose and maltohexaose, while another form produced exclusively maltopentaose from polysaccharide substrates. The third amylase fraction showed usual action pattern characteristic of most alpha-amylases.